I may be in the minority, but I happen to like the move to July. The reason being is that I still have a kid in school, but do not have any relatives in town for them to stay with if me and my wife go out of town. With the July date, we can drop the kid off with relatives for a week in July and we can go to Vegas and play in the tournament (have a short vacation just the two of us). When the tournament was in mid-May we were not able to do that.
Another issue, along the same lines, was when the tournament was in mid-May; without a doubt, someone on the team would not be able to make the tournament due to a high school or college graduation that they had to attend.
I personally have never known anyone who did not go to the tournament specifically because it was too hot in Vegas. I have however, known quite a few miss the tournament due to a kid graduating from high school or college. Granted, I live in a part of the country that is also hot as hell and going to Vegas is a way to escape sweltering humidity.
To be honest, IMHO, the reduction on the numbers attending the tournament probably has a lot more to do with the downturn in the economy over the past years than any other single factor. Basically, a large amount of players do not have the extra disposable income to drop on a trip to Vegas.