IMO, it's the storage. Gasoline packs a ridiculous amount of energy in a very compact, lightweight, portable medium. Also ridiculously easy to "recharge" a gasoline powered vehicle--just pump fuel into the tank.
Batteries can't quite compete with the energy storage density (hopefully modern tech bridges that gap), and the charging problem just sucks. Pumping gasoline into your fuel tank is akin to charging a battery at a rate of several megawatts (did the math for this a while back, would have to dig it up again). Try doing that with a lead-acid battery. I guarantee it will explode in short order.