Are most bikes' paint jobs not as durable as they used to be?
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.