Might be a little more to it than that. The country of Georgia is pretty moutainous. So is Afghanistan. Both seem to get invaded pretty much like clockwork.
Switzerland was valuable real estate when people were invading Italy from the north. Nobody has really done that in a while (except Austria-Hungary during WW1 and they didn't need Swiss territory to do it).
Afghanistan gets invaded because the inhabitants keep coming out and making trouble. If they just sat there, nobody would bother the place.