The cap is there to put the new people logging in into the arena that has low numbers. By doing this it raises the population of that arena. Once the arena population is at 80% of the more populated one the cap on the more populated one will be raised. It typically stays like this for a few hours.
You just have to wait it out and sit in the other arena, logging in and out wont do anything to make the numbers change, but putting your self in the low numbers arena will make it a fraction of a percent higher population, hopefully others will do the same and the more populated arena will be opened. Simple as that.
Caps are put in place to balance the numbers between arenas out so we don't have this ses pool of players in the arena at once.
If you don't like it log on earlier and get a spot in the high numbers arena, or fly on Tuesdays.
P.S.- Insinuating that the game developers are mentally handicapped, is not the right way to go. If Skuzzy or HiTech get in this thread, it is best to drop the point.