I wonder, after seeing the post from Apex Clearing, if part of the reason the brokerages all basically delisted the meme stocks was due to pressure from the option clearing houses instead of the MMs.

Option clearing houses are basically the bookies in this narrative - they make sure both sides actually pay up. They usually don't have much risk, but given the volatility they might be assuming more than usual.

An interesting thought might be that the clearing houses aren't scared of the long contract holders, but worried about the actual counterparties' risk here, which they may be partly or fully liable for in the worst cases.