The understanding was Steam had a different agreement. It was never supposed to be removed there as far as we knew.

so why only us then? Seems very weird for them to do so. I can't see any benefit of them doing that.

GOG indicated different outlets get different agreements, and unfortunately they couldn't get as good of one as Valve. I'm assuming customer base is proportionate to how good a deal is.
Maybe a lot of people signed up since then and Codemasters changed their mind or something...
PS here is the thread with the staff replies.