Why can't all college football start this weekend? Everyone gets 2 byes for the season and the added bonus is that all America gets an extra week of college football.
The short answer is when school starts. A longer version has to do with the allowed number of practices. You'll also notice that some teams, like
Hawaii in this case, have 13 regular season games scheduled.
As I recall, even with roughly the same starting date next season (8/31,) FBS gets two bye weeks next season.