There was some speculation that they didn't have that capability. Brokerage firms should have the ability to restrict margin trading in particular stocks, but

There was some speculation that they didn't have that capability. Brokerage firms should have the ability to restrict margin trading in particular stocks, but what if Robinhood couldn't, at least not on short notice? There could is also the concern about new accounts trading in GME with funds that might be suspect. It's a risk you don't want to take if you don't know your customers and the bubble is ready to burst at any moment.