I think the expiration of Covid-era transfer rules will cool this down a fair amount, and I think this year is a touch fluky to begin with. Even if a bunch of 12-14 seeds didn't win, that still means the 1 seeds had to make it through harder paths against power conference foes and that's not very likely on average.
Also the transfer portal moves players in all directions, not just upwards mobility to power conference schools. Using Southern Illinois as an example again, 4 of their Top 6 players in minutes were transfers.