The reason YC gave for the rejection was that Mexico was an unknown market, and they felt lending in there was too risky for them.
Makes me wonder what was the decision logic to accept this Stablegains, against that background it doesn't make any sense.
Was YC aware of the ponzi nature of this thing and decided to dip in? It just makes no sense.
That's a fair and reasonable reason.
Countries have their own specificities and, very importantly, their own laws an regulations. If you're not familiar the wise move is to stay out.