I thought it was mandatory at release, but added a skip button when the login servers couldn’t handle the traffic at launch. They’re trying to re-enforce it now.

Its just scummy because of the reasons listed above and people lost their refund window when it was optional. It’s mentioned on the steam page. But IMHO there’s a difference between needing a 3rd party account to play the game and linking it to steam which would give them access to more data than you’ll want to share.