Difference is, the wings don't have hinges, which means airplanes doesn't need flexible hoses that can fail and leak between the wings and engines. Another issue are impacts. Airplanes are required by law to keep from hundreds to thousands of meters apart, something that cars doesn't.

And it's not like placing the tank in the doors would save any space. My previous car had the fuel tank right under the rear seat for example, which saved space for the trunk and kept it safe from collisions.

True but the wings are still structural and have the engines on them. Considering how much fual a jet needs you would struggle to find another place to put it. For a car there isn't the same struggle to find a space and if it's a small car you can make a smaller tank and stop more.

Planes what??