Does Steam share a whole lot of user information about an account linked to another gaming network like battle net, Ubisoft, EA launcher, etc if your Steam account is "linked" to these things?

Why does Ubisoft seem so interested in getting me to link my Steam account to Ubisoft? They prompt me to link accounts EVERY TIME I launch Assassin's Creed, don't give you an option to say "no" ... only an option to do it later or something like that.

And they made the window in such a way that it's slightly hard to launch your game without linking your Steam account. Like they made it so anyone launching it just clicking through the login process carelessly would accidentally link accounts even if they didn't want to, and hide the option to proceed without linking accounts in small text in the corner of the window.