Well, it's simple. Fist of all, Cata was return to "raid or die" ideology. Some later xpacks, like Legion and BFA are return to (literally) Classic model, i.e. "MMOs are about grind" model. And since Cata they haven't been adding permanent features - it was about "let's cut this and replace it with that, that will be cut in a next xpack". LFR was last permanent feature in this game. All future ones were about "we don't have budget to support this, so let's just cut it in a next xpack, so players, who like this feature, will just quit".