I am asking specifics in a few posts so as to not get into discussions. Consider this a continuation of bike quality for the price. I find the paint job on my bike to be nice but very thin and fragile. It scratches very easily. When I was a kid you would need to use a jack-knife to scratch the paint. I know there is the rationale that paint weighs and so to eliminate weight they spray the paint on as thinly as possible. Even the rubbery plastic of my U-lock scuffs it.
Price. A combo undercoat/primer, a top coat, and a lacquer/transparent would be the norm.
In the 80s, a nice bike might have had 10 very thin spray coats with multiple clear coats on top, most of which were over the decals/transfers. This represents a lot more work, time, and materials.
In addition, the older bikes would have been steel, whereas the newer bikes are possibly aluminium now which doesn't hold paint as well, due to microscopic differences in how the paint keys into the surface.
I really think it depends on the quality of the bike you buy. Back in the 80's most bikes were of good quality. Today, you can pay more and buy a bike of good quality or spend less and get...what you pay for. That's the kind of world we live in right now. But that being said, there are still some less expensive bikes that have durable paint and durable parts. You just have to do the research and stay on the lookout for a sweet deal.