I have read Livy and Polybius' writings on the Punic Wars and the society of Carthage, as well as publications by modern historians. One thing that puzzled me was the inability of the Carthaginians to rebuild their fleet following the First Punic War. Carthage had, only a generation before the 2nd Punic War, the greatest and most formidable fleet in the Mediterranean. It is mentioned by many historians that by the start of the Second Punic War, while having experienced land commanders such as Hannibal and his ancestors, Carthage no longer had a navy that could rival Rome. Rome had no navy until a few decades before, yet now had superiority over Carthage who had for centuries always had a strong naval force.
Why could Carthage not reconstruct a great navy? Surely it would have been possible, given the great wealth of the city even after the 1st Punic War? Rome also lost many hundreds of warships during the course of the first war, yet with great zeal and determination was able to rebuild by securing funding from allies and eventually private citizens. Was Carthage unable to rebuild her fleet because she was simply unwilling to spend the money? Livy and Polybius tell us a great deal about Carthaginian society, as have many historians, and it seems to be almost the direct opposite of Rome. Citizens rarely fought in wars, with most focused on merchant enterprises rather than fighting. I know a large reason for the victory of Rome in the first Punic War was the unwillingness of Punic citizens and aristocrats to participate in the war effort.
I also understand that a large part of the reason Hannibal took to invading Italy via the Alps was because Carthage was unable to ferry troops without risking disaster, owing the the presence of the Roman navy. Hannibal was to be left without supplies or troops while campaigning in Gaul and Italy, the Carthaginian navy seemingly unable to compete with the Roman. Only a few decades before this would have been unthinkable. Why was Carthage now forced to rely on land forces, traditionally the weaker and less formidable branch of its military, rather than the navy which had always been its strongest arm?
It's not about resources, it's about range. Ancient galleys had extremely limited range, especially if laden with soldiers (higher ship population), so they needed to make fall in a port regularly to restock. This makes it so that control of the seas essentially means control of the ports. The most important crossover point with plenty of good ports between Carthage and Rome was Sicily, for obvious reasons. Just look at the map, it's perfectly placed. This was also true, to a lesser extent, for Sardinia.
As part of the peace treaty at the end of the first Punic War, Carthage had to evacuate all of Sicily, making them lose this advantage. Later, in 227 BC, Rome opportunistically seized Sardinia after rebels requested their help, while Carthage was still recovering too much from wars to contest it. This loss of naval bases made it pretty much impossible to contest Roman naval might, unless some communities with ports on Sicily or Sardinia defected to the Carthaginians, however they wouldn't have just done this, without any incentive. If they had seen Carthage was winning the war, they might have switched (as many Italian communities did in 216), but for that, they first had to fight a war against Rome, and win it. Retaking Sicily seems to have part of Hannibals plan, or at least gain some naval strength back, as he organized defenses for Africa and wanted the other commanders to land in Italy to help him, for which he needed ports (I don't remember all the details of this part and my books are all in boxes, I'll look it up later)
What also needs to be understood is that Hannibal wanted to surprise the Romans, by taking the fighting to them rather then waiting for them in Spain (which was arguably the normal Carthaginian tactic), and by doing it in such manner the Romans did not expect and deemed impossible - namely, crossing the Alps. Now he would fight the Romans on their own land, killing their citizens and burning their crops.
Source: The Fall of Carthage, David Anthony