You can still buy physical PC games, and you can still sell them.
Dude, almost all of them have DRM now. What are you talking about? What am I gonna sell a Steam key that is already assigned to my Steam account? This is something that Valve made happen and no, it wasn't like this before Steam became popular. Consoles still have a used games market, because physical games don't have DRM there. It used to be the same on PC.
I’ve never once heard a claim remotely similar to this, sounds 100% made up