Why must they fight?

I have been asking the girls to clean their room for a week...yes, a WEEK! Given all the junk going on in the house, I was not really getting anywhere in asking...especially when the MIL would go up and distract them or pull them away when they were supposed to be cleaning. The room resembles a house after a bombing, so there is quite a bit of work to be done....the logical choice would be to buckle down and do it right? Nope, not if you are six year old and eight year old girls, then you scream and yell and brawl...productive right? Now they have had to lose even more privlages because they are fighting, not to mention having to clean the room to my standards, which are way higher than what I usually make them do. Why oh why must the fight?