More like they wanted to preempt possible sanctions from the SEC for failing to take action when they observed suspicious behavior by their customers.

Let's be clear about a few things. Brokerages do not care about protecting retail investors, they only protect their customers when forced to do so by regulators. What brokerages do is protect themselves from liability, financial losses, and scrutiny. They have no problem screwing over their customers when it suits them. They will raise margin requirements and force customers to take a loss as soon as their risk models say that they should do so. They will restrict trading whenever it looks like there is a scam, simply because it wards off possible investigations into their business.

What they can get in trouble for, and RH did get a slap on the wrists for already, is working against their customers' interests for the benefit of their business partners. One brokerage I could believe, but I doubt that half a dozen would all do it at the same time and with the same securities.