Why do the Lannisters have such big beds?

Why do the Lannisters have such big beds?

They push two twins together to make a king.

edit: OK, so, apparently this joke was made 10 months ago by some other person. I never knew about that, I thought this was an original joke, so all you people busting a nut because you think I copied someone, go complain elsewhere. I had no idea this joke had already been made.