Exactly, in the rust belt 12 years old the frame is usually badly rusted, the bed sides have no wheel wells and the cabs are rotten on the bottom (cab corners, rockers, etc. The underside of the trucks are usually all rust, fuel/brake lines, brake backing plates, drive shafts, suspension, you name it, they are gone. It would be a unicorn to find a 10-15 years old daily driver that was clean enough to warrant putting an engine in it.
I have seen Ford, Toyota and Dodge Rams broken in half at much less than that, the GM frames seem to hold up a bit longer even though the body is shot.