For the same reason I hate multiple instances... at one point people will want to skip the bosses you have been unlucky on, and it sucks for everybody in the raid that still need loot from there.
Which is also what is happening now in many guilds.. they won't clear on normal even if people would still love to get BoA weapons
It's hard to please everyone.
We have it pretty much solved. Any raider knows that we do 2 farm raids and 3 progress raids (2 hour each). If they want to get a chance on BoA weapons they know we have to reach whatever boss we are currently progressing on (malk atm) on the first 2 hours, that gives another 2 on tue to clear malkorok to garrosh.
Ofc when we get to, say, siegecrafter, it may take ~3 hours to reach. That's ok because 1 hour is also enough for paragons+garrosh. On protectors it was the other way around, we got there in ~30 minutes leaving mon+tue to clear everything