1993 Ford F-150

I am thinking of getting a 1993 Ford F-150 extended cab V8 5.0 litre 2wd but it has rust on the wheel wells. Is the Ford a good idea? why do most Ford trucks have wheel well rust?

It is very possible to have rust under the wheel wells. The question is "how bad?" I would check engine mounts and exhaust for anymore rust.
However being the truck is over 10 years old. you will have some amount of rust unless garage kept and babied.

Check the cab mounts, box cross-members, fuel lines, brake lines, anything that makes it stop and go. The boxes on F150s and up are apparently designed to fall apart at the wheelwells. So long as it doesn't hit the bed it can be stayed with bondo and chicken-wire. Appalachian-American ingenuity.