Only because everyone that wants to enjoy other parts of the competitive scene has to run M+. I’d like source for M+ popularity too. Do you have actual data on this?
Wow always had content for casual players. Leveling, professions that mattered, end game quests that spanned across the world. These activities have been greatly diminished in order to cater to Diablo style players that just want to smash the same dungeons over and over again. M+ is a toxic cesspool too.