I agree that vehicles last longer than vehicles from before the 1990s. But I think that that is because the fluids are better, e.g. oil, and we don't use leaded gas (Which in the long run will gunk up the engine.). In the 60s if you got 100K miles on your vehicle, the engine was worn out (unless it was a straight 6). But if you rebuild an engine from the 1960s and use modern synthetic oil it will last over 200K.
My neighbor is a motor head. He has several cars from the 1960s and they are running over 200K after he rebuilt the engines. Yes- he puts a lot of miles on his cars and he is anal about maintenance.
But if you rebuild an engine from the 1960s and use modern synthetic oil it will last over 200K. I rebuilt engines in my 1960's cars over 20 years ago, and agree. I carefully cleared water passages of metal obstructions, and polished intake and exhaust ports, then used synthetic oil. Ran better (cooler, smoother and stronger than when new. Still running fine today.