Why might hannibal have chosen to cross the Alps to get to rome?

First Hannibal's war with Rome was initially not approved by Carthage and therefore he did not have the support of the navy. Also, just before Hannibal began his march against Rome his own Barcid fleet had suffered a major defeat off the coast of Spain. Finally, while attempting to march via the French Riviera, the Roman consul P. Cornelius Scipio blocked Hannibal's course around Massalia (Marseille) and forced Hannibal to reroute north up the Rhône and the Alps.