Why is there already 2-3 autofills on both teams every game?

I thought the idea of autofill was to make matchmaking faster, but games are taking like 10-15 seconds to find, so surely we don't need to be autofilling half the players in every match, right?

Like, my last team had duo and top autofil, all 3 were also somehow Yi mains. Like, surely they could have each been put into jg role in separate games, right?