The only reason I can see to side with Robinhood and some of these other platforms, is that they were worried about liability.
I tried to short GME when it was at 220 in my Ameritrade account, and it wouldn't let me. The problem with shorting is, there is unlimited potential loss, which is why they require a certain extra amount of funds to be available in your account to short, otherwise you get a margin call. But that begs the question, how much $$ should they require you to have in your account for some of these highly risky, speculative short plays? And if someone doesn't have the funds to cover massive margin calls, who is responsible? I think the trading platforms were worried that they'd assume at least some of the liability in these potential scenarios.
I'm still pissed at the situation, because I would have easily quadrupled my money in less than a week.