UConn got rewarded for playing a tougher schedule. If Princeton would have played a tougher schedule they would have gotten a better seed. Of course they might not have been unbeaten then.
I suspect the problem Princeton has in arranging a tougher OOC schedule is, who is willing to play them? Not from a competition standpoint, but from a "what's in it for me?" standpoint.
If you're a mid-level team from a P5 conference - say, North Carolina or Syracuse or Minnesota or Iowa State or LSU, what do you get from scheduling Princeton? They're not gonna be a "draw" opponent - they're not gonna put fannies in the seats, nor get you on TV. Beating them isn't gonna help your RPI, what with Princeton's Ivy League schedule. If you're one of these teams, Princeton is a "can't win" opponent - you get no credence or advantage for beating an Ivy League team, but you get buckets of embarrassment and snide remarks if they beat you.
When Geno & CD first started building the Husky program, they ran into this problem. With UConn a historically weak program, a lot of other schools saw no advantage to scheduling them. Some schools and coaches (Penn State, Rene Portland) were quite blunt and dismissive about it. Really, the best opportunity an up-and-coming program has for meeting decent OOC foes is a holiday tournament.