There is still a lot of quite useful hardware that isn't supported. For example, the first gen Ryzen is apparently not supported, so then you're having to replace e.g. a Threadripper 1950X which has 16 cores and a 4GHz turbo. A new PC with even equivalent performance would be $600+ and a $500 new PC would be a downgrade.

There is also plenty of hardware that isn't fast but is being used in a situation where that doesn't matter. Some Haswell quad core being used for web and email could continue to be used for that indefinitely. That is old enough that it could be replaced with something newer for less than $500, but the entirety of the replacement cost is still lost money because it otherwise wouldn't have had to be replaced at all.