Since these are IOUs, I can only guess that the exchange itself is selling these. I doubt they have as much real PI as IOUs they are selling (though I suppose it is possible) so they are probably banking on the fact when PI is actually available, it will be worth far less and they will just be able to purchase the difference. Sounds kind of scammy, possibly illegal (depending on jurisdiction) and certainly doesn't inspire trust in those exchanges. But if anyone wants to purchase some IOUs I'll gladly sell some at $300. I have about 900 PI.