Horizon Forbidden West wows in many sections IMO and So does Avatar but its true there's a lack of clear generational leap overall, instead more a refinement of what we saw last gen with more consistency across assets and optional 60fps modes where they would of before been impossible. Its more a half step.
Main reason is diminishing returns in terms of increasing asset detail and density. Alot of increased detail is just lost at the distance they're viewed, meanwhile most devs don't have the capabilities to turn a high quality asset into CGI level visuals. I think at most AAA games current scale it's just too much investement for many... but I think we're about to get a bunch of games which make quite the leap from what we saw last gen. These both show in-engine, so they may look much worse on console (for sure lower res) but lets see.