locked pages, as used for private accounts, have the issue that you either have to either link it publicly and wait for them to wander in, link it publicly and tell them in a comment, or message them offsite to invite them.
linking private pages publicly has the issue that different people have different comfort levels for allowing others in, or asking for access; it can feel foul to turn someone down who you know, but not quite well enough to let them see your private posts. and it can feel weird when people you don't know at all pound on the door. some folks don't want to have to deal with that at all, and keep the page's existence private except to people they trust, but without private messages, linking the account in a way that's globally visible is the only on-site option.
an invite system, possibly restricted to people who follow another page by the owner if spam is a concern, might come in very handy here.