An argument I would make if I we t to court fighting that is that such squatting dilutes the 'USB' brand.
Imagine a world where this 'open' approach gains market share. For the consumer, the net result easily could be that USB, which now is highly plug and play, becomes more like the way ISA cards used to be plug and play: you can plug in any device, but to make it work, you need to do some voodoo (oops, there's more than one device with that PID/VID. Please tell me what you plugged in: X, Y, Z, or something I haven't heard of?")
Exaggeration? Yes, but not completely untrue, and that's the argument I would make.
Whatever you do, you need some entity that prevents multiple manufacturers from using clashing identifiers. That is one of the things the owners of the standard will fight for to maintain, because it is one of the things required to make USB work as well as it does.
Yes, it would be nice if they sold individual VID/PID pairs to hobbyists. But I do not see a legal reason why they would have to do so. Anti-competitive? Maybe, but they will argue that there are thousands of individual vendors in the market.