Websites access is managed on the "Manage users" admin page.
Since user access is set by website, it's a bit weird to find it on the "Manage users" page because this page is by essence user-centric. It would better fit on the "Manage websites" page, or on an independant page.
If you want to keep it on the "Manage users" page, you better have to switch to a "website access by user" model.
I think it's OK as it is... we can revisit later for sure, but does not imho deserve own ticket.