Well, for something that happened 2 millenia ago, the extent of the support of the Carthaginian senate to Hannibal is still hotly debated academically. From what I read, there is some ( admitedly shaky ) evidence that, while the Carthaginian senate was not in love with the idea of another war with Rome, they saw it as something Rome had forced unto them ( in other words, Rome actions in Iberia had to be sooner or later be stopped if Carthage wanted to have a empire there ) and they were more that willing to support Hannibal after the war was on. But:
a) Carthage, unlike in the 1st Punic war, was never in control of the seas. This had various causes ( the loss of Corsica and Sardinia after the Mercenary war was a heavy blow to the Carthaginian war navy, that had relied on those islands forests to make their ships ... besides the fact that, until the war started, Carthage was bound by the peace treaty with Rome to a skeleton navy, only good for piracy control ) , but this meant that Carthage was never really in a position to send armies to Italy besides whatever could be marched on from Iberia. There is a reason why Hannibal and the other Barcids later didn't just caught a boat in Iberia and disembarked in Tuscany or Capua
There is actually some evidence that the original plan for the war was to march troops through the Alps, gather support from the Gauls, march to Rome and then send whatever navy they could muster to blockade Rome by sea at the same time Hannibal marched in the direction of Rome ( given the panic that Hannibal marches to Rome created, some enemy sails could had simply tipped the mood in Rome to a negotiation ) . The Roman navy made sure that never happened, though and Hannibal had to ... improvise.
EDIT : Adding to that, the fact that the Romans had the control of the sea meant that
they could drop armies where and when they wanted either in Iberia or Africa ( like they did
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), so Carthage had to keep garrisons pretty much everywhere ...
b) Numidia. Carthage was well aware that, as it actually came to be, Numidia was not to be relied on as even a neutral player in a war with Rome. Carthage tried to divide the Numidians and keep them divided and hireable if they couldn't put someone firmly on their side rulling it, but they couldn't simply pretend that there was not a Numidian dagger on their backs at all times.
c) Carthage was still recovering from the Mercenary war, a conflict they had with the hired mercs of the 1st Punic war when they were not paid for service ( with a very visible hand of Rome stiring things ). It is not surprising that the Carthaginian senate was not exactly in the mood for a 2nd Mercenary war, and they did not hired as much mercenaries as in the previous war.
My personal opinion is that it is not that Carthage didn't wanted to help Hannibal, they just were not willing or able ( more unable than unwilling TBH ) to provide for the resources needed to defeat Rome. Their navy proved unable to fight Roman sea control, so it is not that they could actually disembark troops in Italy to help Hannibal or even reinforce Iberia easily and they had Numidia that could flip against them at any moment. In the end it is a huge testament to Hannibal skills and fear projection that he could keep operating for almost 2 decades after the war was basically lost due to the fact that , besides Hannibal, Carthage could not put a credible military threat on Rome proper. ( The only real mistake you can point to Hannibal leadersip was underestimating is brother ( not Mago
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) and let the Romans beat him before they could join forces ).
OTOH this manga Hannibal has quite the point. Regardless of what he felt about the Carthaginian leadership ( RL Hannibal never showed any sign of being more than a staunch patriot ... not necessarily in line with the government of the day, mind that, but a patriot that would leave everything to defend his motherland ), if Carthage fell he would be forced to acept defeat anyway even if he was not beaten in battle , like his father had to do in the 1st Punic war. So, the least bad course of action was just to do what he did ( will do in the manga ) and get back to Carthage to try to beat Scipio out.
Anyway, to Zama we go. I suspect that we will have some serious bromance soon
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