Main issues are economies of scale - Lots of AVRs out there. Joe public wouldnt know the difference between 4k 60Hz 4:2:0 and 4k 30Hz 4:4:4 except for what the sales guy at Curry's tells him or if he thinks that he is a tech-head whatever the interwebs tell him is the best. For 99.999% of the population 4k is 4k is 4k or its whatever your PS4Pro / XBone can allegedly do.
This leaves the door open to Amazon sellers to sell whatever garbage they want making all sorts of wild claims - HDMI Cables being HDMI 2.1 compliant, devices that are HDMI 1.4 but can do 4k 60Hz : HDR10 : 4:4:4 : Dolbyvision : HD Audio.
You really need to look at some of this stuff in detail to actually understand what they are selling. The devil really is in the detail. Or you ask somebody like
@Joe Fernand for advice as he sells this stuff daily. He is not going to sell you garbage, but its not going to be pound-shop cheap either.