I understand your concern based on how corporations tend to run these days, but this is a lot of speculation. It’s good to be skeptical though.
My guess is that they want to use a single account across more services unrelated to GOG, akin to the way google SSO works for gmail, YouTube, drive, etc. If the account is owned by a subsidiary that might not be possible for other subsidiaries to use the same account per data regulation rules.
I actually played it with my son coop a decade ago when he was quite young, he’d sit in my lap and we’d each have one hand on the controller. We played it through that way and had a blast. I remember him being quite scared at some points, and the game was an emotional rollercoaster, but we very much enjoyed playing it together and I could see it working as a coop game.
I had to stop playing Half Life Alyx when it got to the dark flashlight bit with zombies jumping out at you. Nearly gave me a heart attack. Definitely couldn’t handle it IRL. edit: autocorrect