It’s because once you go past the easy modes the MM community falls apart. Even mid-level NFs can be an absolute disaster and can feel like pulling teeth with MM blueberries. If Bungie could sophisticate their mm to be able to vet players by experience - like say having a KWTD option in the fireteam finder that blocks people from joining that don’t have a certain amount of full clears - then I could see a mm option for standard and even master raids & dungeons. But I can’t see it ever working with the current in-game mm/lfg systems.