Elemental Bosses Seem the Same All Day

If people are supposed to get all 4 Dimmed Elements, I wonder why Blizz made the bosses stay the same element all day instead of changing more frequently? I've been logging in every 30min or so for about 5 hours now and it's Ice in Badlands and Fire in both Kalimdor locations. I need Air so idk when I'm going to get it.