Guilds that raid on Sunday when they only raid 3 days a week, and have no obligation to pick any day. Such a boring day Sunday to commit for.
Nobody raids on Saturday morning. Or virtually nobody. Most of those that don't, do have the time to do it, and it's the most productive raid time.
And best of all, people thinking wiping is tiresome. It's virtual, and learn to make gold. If you spent more time on a kill it's the same waste.