Exactly you don't buy the slot, so Riot has even more right to choose if you're in or not. I think if they didn't let them in is because the problem was very serious.
So you're suggesting 2 options,
1 Let the roster be picked up by another team. Alright but then you're selling a slot and having a massive auction to see who picked them up which can lead to several big issues again, inflated salaries, or even orgs not entering the game and waiting for opportunities like this
2 Riot pay the players, alright but how is that competitively fair? The organizer can't own a team if you know what I mean