Few people are insane enough to go AI with something like middle connectors or random crap...so you gotta figure, if there's a lot of folks going AI, they've all got high cards, and if everyone has high cards, it's far less likely they'll hit anything to beat you. For instance, KK vs AK vs AQ vs QJ gives you around 60% to win, hugely EV.

In other words, if I'm holding KK, the more people AI the better - the more likely it is that they've all got a single ace (and are also playing eachothers straight outs)