I'd say the cost to benefit to Mythic isn't really worth it any more when a casual guild can get loot with the same or higher ilvls if it titanforges.
Why spend 1000 hours wiping when you can just get your N and H done easily and potentially get the same loot?
Edit: And I say this while being in a relatively casual (3/10M) guild. My ilvl is 917 (906 equiped) and I've only killed M skorp 3 times and M chrono/trill once). Yet, I probably have around the same ilvl as most hardcore M raiders.