I've been listening to the History of Rome podcast and Carthage apparently was able to send fifty thousand troops to defend Spain. Why didn't they send large scale reinforcements to Hannibal? Or send in a large force to retake Sicily? If anybody could answer this I would be grateful! I've been wondering this for like a week.
The invasion of Italy by Hannibal can be considered a Barca family enterprise. It was mounted, financed and reinforced from Spain, which was almost a personal feud of the Barcas.
It is not even certain that political elite in Carthage was consulted by Hannibal before he attacked and razed Saguntum, the casus belli for the start of the second punic war.
After that, the notables back in Carthage were very ambivalent about supporting Hannibal. Many of them were political enemies of the Barca, and many other did think that the time was not ready for a renewal of hostilities with the Romans.