powerful teams with stacked rosters want one portal window at a time when making a move would not be good for the players from a timing perspective. Powerful schools want to lock their players in place as much as possible.
Weak teams want the portal to open as soon after the end of the regular season as possible so that they (and the players) have time to find a new school and get enrolled in time for spring practice so that they (the players) maximize their chances of succeeding at the new program...which, BTW, is in the interests of the HCs of the weak schools, as well.
Guess what Kirby Smart wants?
Guess what Clark Lea (HC of Vandy and one-time Ucla gofer) wants?