I sold GME for a tidy profit on RH while buying was disallowed. Not hypothetically; I really did. Are you saying RH should have forced me to hodl? How would that have been a better customer experience?
In that other reality you are proposing, Robinhood gets declared insolvent and enters into receivership at the market close. Your entire investment account gets frozen for a year or so, until the insolvency process is finalized, and you can finally get your assets back.