I can offer you an insight into the second question - the topic itself is incredibly complex and made up of a multitude of layers but I will try to answer it hopefully. The context under which I would answer the question is in the discussion of aristocratic competition. The laws that you mention are sumptuary laws, or leges sumptuariae as they were called by the Romans (Cicero. Fam. 7.26.2).

 

Sumptuary Laws

The popular definition of sumptuary laws within modern scholarship is those laws that regulated consumption and display and such laws are actually attributed to the second century BC. However, it is actually during the Second Punic War in which we begin to see the concept of restricting the personal expenditure of elite (and that is important) individuals within Rome.

 

Sumptuary Laws During the Second Punic War

It is well documented that during the Second Punic War Rome faced incredibly financial strain, and from 215 BC onwards we begin to see a variety of measures introduced in order to raise funds. Those measures include: debasement of bronze coinage (aes grave), a measure which failed resulting in the introduction of a completely new coinage standard in 211 BC (denarius); borrowing grain and money from Hiero II of Syracuse (Livy. 23.21.5); doubling of the tributum with the normal amount being levied immediately (Livy.23.31.1); the creation of credit and national debt (Livy. 23.48.4-12, 24.18.10-11); the ceasing of temple maintenance contracts and providing of curule horses (Livy. 24.18.10); widows and orphans cared for via state credit following the donation of their possessions (Livy. 24.18.13-14); individuals being ordered to pay for the funding of sailors (Livy. 24.11.7-9, 36.35-6); valuable metals being borrowed from the ‘gods’ (Livy. 27.10.11-13); women being summoned to contribute money from their dowries (Livy. 27.37.9-10); and the ager Campanus being rented out (Liv. 37.11.8). Roman citizens also took it upon themselves to provide finance to the state with measures including: deferring payment for contracts until the war was over (Livy. 24.18.11); deferral of payment for slaves manumitted in order to serve in the war until the conclusion of the war (Livy. 24.18.12); and equites and centurions opting to receive no pay for their service.

The important note to consider is that whilst the Roman state was poor, such measures suggest that its citizens were infact quite wealthy, otherwise said measures would be pointless. It is from such measures that see three laws that could be considered sumptuary by nature: the lex Metila de Fullonibus, the lex Claudia and the lex Oppia.

The lex Oppia is what I would highlight for your question and it gives an insight into the possible reasons for the further sumptuary laws in the second century BC. The lex Oppia of 215 prevented women possessing more than half an ounce of gold, wear parti-coloured garments, or riding in a carriage within a mile of the city or towns except for religious festivals (Livy. 34.1.3). Now, on its own and given the financial struggles of Rome at the time you could see why such a law would be implemented. However, the lex Oppia was one of eight measures taken against women during the Second Punic War. Those measures include: a senatus consultum restricting female mourning (Livy. 22.55.6-56.5); enactment of the lex Oppia (Livy. 34.1.3); requisition of the assets of widows (Livy. 24.18.13-14); a senatus consultum restricting foreign religious activity (Livy. 25.1.11-12); an aedilician trial and exile of women for probrum (Livy. 25.2.9); enactment of the lex Atilia (Gai. Inst. 1.185-186; Ulpian. 11.18); requisition of assets from women for the public treasury (Livy. 26.35-36.12); and requisition of assets from the dowries of women (Livy. 27.37.9-10).

I won't deviate too far away from your question, but you could view such measures taken as a method of curbing the financial and social independence of women. Brunt estimates that between 218 and 216, the Roman state mobilied 108,000 men with up to 50,000 of them being lost (Brunt, Italian Manpower, 1971: 419-420). Livy reports in the census of 234 BC that there were 270,212 men and in the census of 209 that there were 137,108 men; a total loss of 133,104 (Livy. Per. 20, 27.36.7). It is clear that a lot of women suddenly lost their fathers, brothers, husbands, and other male family and thus became wealthy through inheritance as well as becoming independent. There is evidence within Plautus and speeches of Cato to suggest that wealthy women were something to be feared, in which why it seems reasonable that such measurements were an opportunity to remove wealth from women. The fact that in 195 BC the women stormed the forum, whether or not it was done under the organisation of men, shows that Roman women had a sense of independence now. As you can see, this is how laws could be used in a political manner.

 

Sumptuary Laws During the Second Century BC

The introduction of sumptuary laws and their purpose has traditionally fell under three aims: an attempt to correct morality within Rome, the restriction of the political influence of the equestrian class, and the protection of family patrimonies due to an increase in aristocratic competition. The second reason, the restriction of the political influence, is one that seems the most likely to me. The first reason is plausible, but if you look at some of the clauses within sumptuary laws you have to ask yourself what does this have to do with morality? For example, the lex Fannia included provisions against purchasing fish that cost more than 2½ drachma (Ath. 6.274c) and allowed the use of only one hen that had not been fattened (Pliny. Natural History. 10.139). A senatus consultum issued within the same year prevented the use of foreign wine yet allowed local wine (Gellius. Attic Nights. 2.24.2). The third reason seems unlikely because sumptuary laws never targeted significant expenditures, such as houses.

I thought it was a possibility that senators were also trying to profit from their own agricutlural efforts which would give reason to why such specific dietary requirements. For example, the lex Fannia allowed only for the use of a single hen that is not fattened (Pliny. Natural History. 10.139) which is interesting because according to Varro (Rust. 3.9.16-21), fattened hens were imported from North Africa. The senatus consultum enacted alonside it restricting the usage of foreign wine but allowing native wine furthers such idea (Gellius. Attic Nights. 2.24.2).

Back to the question however, why would senators want to restrict the political influence of the equestrian class? Firstly, senators were restricted in the ways they could earn money allegedly. The lex Claudia mentioned previously restricted them from owning ships that could engage in significant maritime trade, and senators were expected to earn their money through owning land and farming (Cato. Agr. Praef. 1-2). One does raise a question of whether senators were actually restricted. It is said Cato bypassed the lex Claudia by loaning money to partners within a maritime-trade company, with him having a share and being represented by his freedman, Quintio (Plutarch. Cato Maior. 21.5-6.). Cicero in fact regards the law as being a dead law by 70 BC (Verres. 2.5.45). Anyhow, such factors mean that the equestrians had access to a variety of methods of earning money when compared to the senators - the senators could not restrict their ways of earning money, but they could restrict their methods of buying political influence with that money.

Hence, sumptuary laws provided that opportunity to restrict the equestrians. We know from Cicero that banquets were important political tools, having defended one of his clients charged of using banquets in order to increase his election chances (Mur. 74), despite admitting how integral banquets are as a method of gaining electoral support (Rep. 4. Fr. 8).

Such laws also make more sense with further context. For example, you have the lex Orchia Sumptuaria (Macrobius. Saturnalia. 3.17.2-3) in 182 BC which limited the amount of invited guests, in 181 BC you have the lex Cornelia-Baebia de ambitu (Livy. 40.19.11) which was regarding electoral bribery, and you also have the lex Baebia de praetoribus (Livy. 40.44.21) in 181 which alternated the amount of praetorships between six and four, and in 180 BC you have the lex Villia annalis (Livy. 40.43.7) which introduced requirements on magistrate positions. It is clear that within this period there was political tension that led to the enactment of such laws. Further down the century, you have the lex Fannia sumptuaria (Macrobius. Saturnalia. 3.17) which restricted spending amounts, and in 159 BC (Livy. Per. 47) you had the lex Cornelia-Fulvia de ambitu which was a law against electoral corruption.

Thus, when you ask why were laws passed to restrict the luxurious tastes of Rome's richest citizens. To give a simple answer, I would say that it was more an opportunity to protect the political elite against those of the equestrian status who had taken advantage of Rome's properity following the Second Punic War.

 

The whole topic really ties in to a much bigger topic regarding aristocratic competition and the rise of the individual during the period. It is hard to try and summarise such topic into one post because a lot of it is linked together i.e. to suggest one idea, you need to introduce other ideas first. Following the Second Punic War, Rome went through a process in which political and social barriers began to be pushed to their limits, the question you ask is within that topic and can be answered - but there is a lot more to the whole picture if that makes sense. Hopefully this is a good enough answer, but if you have any further questions feel free to ask.