He managed time and time again to attract Iberians, Celts, Gauls, etc. to flock to his cause, but most reinforcements sent from Carthage were directed to their holdings in Iberia. Could he not have arranged to have more reinforcements himself, or someone from his political side in Carthage arrange for more African reinforcements sent to Italy?
One or two ships did get to him from Africa, but Rome very much controlled the sea's in the 2nd Punic War and the divided nature of Carthage's politics meant there was no real will to help Hannibal out, it's unclear just how much approval Hannibal even had to start the 2nd Punic War.
Logistically a ship would take several days to make the journey and would need to rest its crew and take on water at least every 48 hours if not more which requires safe territory. It was standard practice to beach a ship at the end of each days journey and stick close to land, the rowers and passengers would need good fresh water in order to keep going. This would make landing in Sicily difficult as it was Roman territory at the time.
My source is somewhat unclear how Hannibal returned to North Africa so easily sadly.
Sources - Adrian Goldsworthy: The Punic Wars (good details on naval travel, logistics and the Punic Wars themselves)
/u/scipioasina and /u/XenophonTheAthenian also answer this question very well here:
https://www.reddit.com/r/AskHistorians/comments/1scpwe/why_was_hannibal_never_sent_reinforcements/