Sure, we could do it more than once a year. But they could run hot reality shows back-to-back, too, and you've seen the result of that (LCS3, anyone?). The truth is, dilution happens.
I think once a year is plenty enough. It's expensive, tough to plan, and quite frankly, getting me to go on a personal trip more than once a year, after all the travel I do work-wise, ain't gonna happen.