Currently, any user who is part of workspace can view the list of workspace members under "People" tab  - https://bitbucket.org/workspace_ID/workspace/members/
The suggestion here is to restrict / limit the user who can see the complete list of people in workspace. Eg: Users can only view the other users on the same project and not all users in workspace.

Workaround

Currently there is no known workaround for this behaviour.