hannibal didnt follow through, why?

He didn't know how to make siege weapons. He just went around on the peninsula for a couple years then was called back to Carthage during the 2nd Punic wars.

 

It wasn't a couple of years.Hannibal and his army stayed in Italy for 14 years.
Also, i don't think that Carthaginians had such lacking siege technology. I believe there was a number of cities stormed by Carthaginians for sure. Besieging Rome ,however, would require a huge shift in Hannibal's plan.His army was more or less unable to undertake such actions, completely surrounded by Rome and its allies. Hannibal's plan was to take the Italian cities on his side in order to weaken the roman legions and disrupt considerably Rome's supply lines. For example, Campania was one of the ,most fertile regions of Italy and Hannibal was very concerned on keeping important cities, like Capua, under his control.

 

Actually, the Second Punic War started because Hannibal took a Spanish city allied to Rome by siege assault.