They might be simply preparing for that eventuality, and when the law changes they can quickly react. Apparently in the e-mail that the users got, they are claiming that nothing privacy wise will change, and that might indeed be true for now.

I think that also breaking the law might be easier. EU might not bother anymore penalizing them for a member that's already leaving, and UK alone will have very little force imposing penalties on an US corporation.

Yeah, the UK didn't fell out of the EU. There's a transition period that just started and right now, there's basically no change yet.

UK citzens are still EU residents for now, the UK hasn't actually left yet.

The word "now".

The UK is following EU rules and regulations at least until the end of the year. After that point, it can pick and choose, based on negotiations for trade agreements or whatever other reason pleases it.