I am NOT giving the site; I have never heard of it. But from what I see, you HAVE to sign up to their site for the key. I am not sure what they are doing…farming emails??? If I am wrong about this, let me know.
I got it for free on Steam (Europe here) so… maybe It’s just restricted for their weird giveaway-email-key-thing?
So weird because, as you said, It’s just free on Steam… like right there…
I know which site you are referring to and I made an account there 1-2 years ago … I even forgot about it. They don’t spam with mails at all ( I haven’t tweaked any options in their platform at all - I don’t bother changing notifications by e-mails until it gets pretty annoying ), I’m pretty sure haven’t gotten a single one since the registration one.
But like @Madway explained … steam activation doesn’t give you anything.