I’m probably insanely late to this, but here’s my theory on why the people of Gravity Falls are Wack.

I think it's because of the Society of the Blind Eye, since it was stated that they have side effects that effect how people act, so maybe the memory wiping made them slightly crazy but not full out insane, just mellow enough to blend in to society. Or it could just be because it's a "kid's" cartoon