Making the game more accessible for casual friendly isn't the problem. I always find it funny that the people who claim this, usually are only doing lfr and normal at best, let alone heroic clearing and mythic progression.
The game's current decline is basically because it's a 2004 game and time's change. The MMO genre just isn't as popular as it once was and teens today are getting into other games like Fortnite, Apex and most likely soon there will be another type of genre and Battle Royale's will die down too. Instead of catering to some hardcore group that doesn't pay the bills, Blizzard is doing right by making the game more casual friendly(I dont see how it is anymore today than it was in WotLK) and they should also be planning on moving Warcraft's format to a different genre imo, maybe one that suits the franchise better than chasing trending ones that fizzle out after a couple years(I personally would love an ElderScrolls/Witcher like Warcraft game)
And with HotS(blizzard AllStars is what I remembered the name being), they chased after a trend that was starting to die off. It would be like if Blizzard announced a Blizzard Battle Royale today, it would come out at the fall of the genre.