Having been there during the competitions, there aren't that many cheerleaders.
I think the real reason is (a) that's the end of Value season, before Peak season starts, and (b) with day-by-day rates, bargain hungers have to *end* their trips by the 10th, whereas in years past they could merely *check in* by the 10th.
Together, this bunches up the bargain-hunters in that last full week of Value season. There are still plent of Mods and Values for President's Week when rates are in Peak season, but I'll guarantee you the parks will be busier then!