Same reason why they enabled core unlocking back in the Athlon/Phenom II days - there was a good chance unlocking more cores wasn't going to yield a good/usable experience, because those cores were locked away for a reason. But people opted for it anyway. I'm sure some of these motherboard manufacturers are just trying to get rid of old stock. As of right now, there are hardly any PCIe 4.0 devices to test with and by the time there will be, the warranty might end (and for customers who bought the board prior to Zen 2, the warranty is likely already over). People like having/doing things when they're told they can't, and they retaliate twice as hard when they actually got to do/get what they wanted, only to have it taken away. This is why underage drinking exists lol. But you said it yourself - there's virtually no gain. Nothing is stopping you from going to X470 for a lower price with a minimal loss. There's backward compatibility, so you're not forced to do anything.