They have no choice, remember their clearing house sets the liquidity requirements and the government also has a few others but I won’t go down that road. All the main clearing houses raised everyone’s liquidity requirements, this forces RH, Merril, Charles, Goldman, Fidelity and everyone else to rebalance their books.
Also your primary broker can sell any position you have at any time to fix their books... it’s in the fine print when you open an account.
Regular equites are no different than options as the market moves up and down it forces your broker ( think RH or whoever) to constantly rebalance and show the clearing house they have the available $’s on the books to cover any loses. The larger the volatility the larger the collateral they need in their bank at all times.
The reason they restricted these names was because retail was buying more than RH had the ability to hedge with the liquidity they had in their bank accounts. No money in bank account means clearing house shuts you down and in turn shuts down retail buying. The reason only selling was allowed was to bring money back into their accounts.