> limitations were as a result of Robinhood et. al. being unable to cover the risks involved in providing instant trading capabilities for a stock as volatile as the ones that got restricted.

Yes RH had to cover more, because the clearinghouse was also starting to be stretched by the risk from the violatility. If the hedge funds go down, the clearinghouse wouldn't have been able to front their cash, and they would've gone down as well.

You're also missing the point that the clearinghouse firms didn't just ask for more money from brokers. In many cases they told brokers to step selling these securities.

There's increased risk on both sides, but the long side is at least finite (and probably there's not much margin). The short side is not. The unknown risk the clearinghouse needs to worry about is the short (hedge fund) side.