Raiding mythic and being a "progression" raider requires so much more in Legion. M+ grind, AP grind, legendary grind and consumable grind are not for casuals andI think lot of guilds are now realizing that they don't have what is needed to belong to that club.
Playing less, more casual and toning down expectations might help. Mythic is not for everyone and in Legion it is only for the very hardcore dedicated.