No, they didn't, because the senate did not and could not pass laws. The laws that you're referring to, such as the Lex Claudia, were passed by the people in the assembly. The senate's ability to issue binding commands was indirect. The senate issued decrees, which were non-binding orders given to magistrates, although in practice they were always carried out (I can't think of an example of a senate decree that wasn't eventually upheld). Because the magistrates had potentially a very wide jurisdiction these decrees could be issued on quite a large range of topics, but typically they were essentially administrative, and it would've been rather an inappropriate use of the senate's decree and a magistrate's power in a lot of cases to expect them to cover sumptuary subjects. The senate could also issue decrees, usually to a consul but sometimes to a tribune (and, if no one else was available, in extremely rare cases to a praetor), to promulgate a law in the assembly. Most consular laws have as their origin senatorial decrees. Laws like the Lex Claudia are not often on that list, although quite frequently these (typically tribunician) bills were strongly supported by important members of the senate, especially consulars. Q. Claudius' Lex Claudia, for example, had as its main supporter the consular C. Flaminius, and the Gracchi were both supported by consulars or actual consuls (Crassus, Scaevola, Appius Claudius, Fulvius Flaccus, etc.), and Ti.'s land law probably had the support of either a majority of the senate or a substantial, and very influential minority, at least until Ti. interfered with the senate's authority over the treasury by promulgating his law to the assembly about Attalus' fortune.

The senate, however, was a self-regulated body, effectively, and it did self-regulate. The censors, aside from assessing military manpower every five years and performing the necessary rituals for the lustrum, assessed the suitability of sitting senators to their position--not office, as senators were not officials, but merely private citizens. You could think of the senate as a club of former elected officials and, in the early period at least, people like Scipio who were related to elected officials and considered meritorious enough to be in the club despite not having held elected office at the time of cooption, who advised the current elected officials. Membership in that club corresponded closely enough with the aristocratic families as to make the two terms effectively synonymous. Aristocracies tend to be self-regulatory, because the exclusivity of the aristocracy needs to be maintained, or membership in its ranks becomes meaningless. This is a prestige class, and in a society like Roman society where aristocracy was very poorly defined the importance of self-regulation becomes even greater. Thus, while the senate did not pass laws regulating its members' private behavior, many prominent senators sponsored these laws, and there were many other mechanisms, formal or not, by which the aristocracy maintained its own image. We can speculate on the reasons why individual senators might have supported laws that, purportedly (though, if you look into it, not necessarily in actual fact), were destructive to the senate or its power, but that's not really a historian's problem, and there's not really any way to know without asking, and they're dead. There's every reason to believe, for example, that Ti. Gracchus and his consular supporters legitimately believed that the privatization of public land in southern Italy was genuinely necessary, not only for the well being of the people, but also for the health of the state, which they believed was running out of military manpower. There's also every reason to believe that some element of aristocratic self-regulation may have influenced the behavior of some of Ti.'s supporters, or Claudius' a few decades earlier, in that imposing stricter rules on the aristocracy makes it more prestigious (in this case Ti. is a bad example, since Stockton showed that there's little reason to think that the people that Ti. targeted were mostly senators at all). There are lots of reasons why a senator might have supported the Lex Claudia or the Lex Sempronia, and no doubt most or all of these reasons are present in the many senators who did support them. If you want to untangle that you can try asking them.