Well my raiding guild has actually returned in bfa recently again, so thats not true for everyone. But the decline within this xpac has been significant indd. But thats not realy the games fault.
Its the community. People are just fed up with wow for playing it for over 15 years. People also expect that the game gets better each year. Which it wont cause the wide span of acitivties blizzard has to implement these days are realy enormous. Its hard to please people that consume more then their given. People crave for more more and more. Theirs no company in the world that can make this happen im afraid. Its the era we live in