You are the product, and allowing you to hide your profile makes you a less valuable product to the customers (recruiters). Until paying customers start complaining that their response rates are too low because there are too many inactive/unresponsive profiles, this won't happen.
What I hate the most are the cheapskates recruiters that don't pay for premium and spam you connection request not being able to send direct mails.
I don't mind being connected with relevant offers, that's what I signed up for. But then there are those low rate recruiters sending shotgun requests, asking for connecting and then asking me to do their job (you know, that'if you know someone interested' part) with mass request that are not even close to my listed skillset.
I don't understand how people can benefit from employing them, if they can't even match skills too job most prospects sent to interviews will be a waste of time for both parties involved.
You are the product, and allowing you to hide your profile makes you a less valuable product to the customers (recruiters). Until paying customers start complaining that their response rates are too low because there are too many inactive/unresponsive profiles, this won't happen.