For me, the interest in retro bikes, is mostly just aesthetics, I love the old frames, the colour schemes. There's also some other positives to the retro bikes, some of the componentry and standards have stood the test of time. I'm not interested in retro stuff that isn't well functioning. Luckily a lot of the older stuff still is, square taper still beat any other drivetrain on pure longevity, v brakes are still the best option if hydraulic isn't an option, 26 isn't quite dead. So half aesthetic half the fact that it's bombproof at a low cost. Unless you're buying the boutique crap.
I agree that there are many post 2000s bikes that are very much Retro, even bikes made after 10 that are pretty damn retro in spirit