You're making assumptions that it was the liquidity provider who pulled the plug and not the much more likely option that it was Robinhood pulling the plug for liability reasons.
Tastytrade also restricted trade in the same manner. They send a mail to all customers and made it very clear that it was Apex Clearing who forced their hand. It is very unlikely that something different happened at Robinhood.
They've already been sued by retail investors who have lost their cash in the past and courts have already shown themselves to be somewhat partial to "the gamified interface just made me spend $1k I could barely afford because it was so fun!" arguments that RH is liable.
This is a much bigger deal, some (not hedge fund!) people are going to lose a crapton of money on it, and people are probably going to sue them once that happens.
You can see this discussed elsewhere in the thread.
