So, lets look a bit at the state of m+ in this expansion.
Season 1 was very good in terms of balance, and we had a lot of tuning there which was good. Start of season 2 was also very good until patch 10.1.5 hit and brought Exodia comp which was the worst season ever also lowest number of players because of that.
Then they nerfed mage and shadow priest, and season 3 started with diverse specs in m+ and there was no established meta. All good. Until they decided to buff mage and SP again, and thus making a comeback for Exodia dps comp of mage, SP and aug which was again dominant at the end of season. And they even made it stronger with god strong DH tank.
And then we have season 4 now with same story again. Those 3 dps specs continue domination for 3rd season in a row, plus DH tank is played by 95% of people. And that comp makes huge pulls possible, so other specs which cant contribute to huge pulls a lot become unwanted by anybody.
So when we look at these 3 seasons it seems Blizzard just dont care anymore. What happened? Why they gave up?
In my oppinion its better that spec is undertuned and opens possibilities for other specs to play the game, like we had in S3 at start, than making spec as SP so much overtuned and thus closing the door for other dps specs. Also with DH tank, why making it so insanely strong? They could see very quickly how it would affect other tanks, and not just tanks but also affecting dps comps a lot. And yet they decided to do nothing.