But they do, frequently. In fact $250 is on the low end of what they are actually selling for on ebay pre owned.Just because someone is asking that doesn't mean someone will pay ... you can get a R5 3600 for less than that, no one will pay $250 dollars for a 7700 ... $100-150 maybe, but not $250.
Probably because for many people with sky/kaby lake systems, a 7700 or k is about all they can upgrade too.
Sure a motherboard and CPU would be a better option, however its clear people are actually still upgrading to 7700s at those prices based on sold eBay listings.
I must have misread about your new display. I thought you were looking for 4k tvs, but i didn't see oled. 4k tvs can be bought for like $300ish for a low end model around 50inch or so. But oled, that drive cost up, a lot.