First, apologies if this is mentioned somewhere else, I did not find it when searching.
Remember when Cata launched and Blizz said they were going to make hit rating more interesting, that it would scale in the later tiers meaning we would need more hit rating to for example never miss Deathwing rather than Chogall.
What happened? Is there any indication they changed their minds? Or have they just not implemented it without comment?
They've said nothing and as such nothing has happened with it. It's an abandoned idea.
My best guess is because it'd be way too difficult to figure out a method to communicate to players what you would need for each raid, especially considering people just look at Hit as a number-based rating instead of a percent. For example, if you needed enough hit rating for 8% hit in Tier 11 raids but then you needed more for Firelands for the same %, such that you'd have 11% hit in Tier 11 but the required 8% for Firelands, how would you communicate that through a display to players?
It just wouldn't make sense to have +8% hit but "oops not really!" in Firelands unless they actually put in a -Hit zone aura like they did with Icecrown Citadel and Dodge, and I think everyone would agree that would just be lame.
It's easy to see why the idea was abandoned.