> They let their customers sell which was probably a fiduciary responsibility.
Given the context of gamestop's stock, only allowing to sell stocks is the exact opposite of protecting the customer's best interests.
I mean, the high demand for gamestop's stock was motivated by the rally behind a retail-backed short squeeze, where hedge funds were reported to have massively shorted gamestop's stocks. Barring customers from buying more gamestop stocks meant they were unable to strengthen their positions and thus profit from the short squeeze,and pushing them to sell represented a pressure to kill off the short squeeze, thus acting on the exact opposite of their customer's best interests.
Then there's the reported news that one of RobinHood's new backers ends up being one of the hedge funds that stood to loose massively due to this retail-backed short squeeze.
An obligation to maintain the market for a stock because a portion of it's owners are your customers would be a bizarre responsibility.