Romans pulled on him the same trick Greeks from Syracuse pulled on Carthage some 200 years prior when Carthage was laying siege to Syracuse. The Syracuse tyrant took almost all men he could spare, sailed to Africa and rampaged around Carthaginian lands which forced the force near Syracuse to withdraw to face him, thus saving the city. Same thing, just Romans won the battle in Africa and Rome was never directly threatened (although Hannibal was "at the gates" he never attacked).
Simply he did not have the manpower and resources to do so. He could only hope to turn all Latin people to his side and to gain a port so he can get reinforcements. Its amazing what he was able to do with such a little force deep inside enemy territory. Romans were also not sitting on their asses, but were constantly following him around, harassing and taking back cities he just left.
The thing that interests me more is why the Greeks didn't seize the chance and ally with Carthage to finish Rome off, seeing as Rome was a threat to all of them. Maybe they didn't take them seriously yet.