My boyfriend has almost nothing "personal" on his Facebook, why does this bother me?

His profile pic is some anime character, he has NO photos of himself, family, friends, me - not even his car or his dog.

His bio is minimally filled out, he DOES have our relationship status, but all he really posts are memes and videos to science stuff he finds interesting.

He said he doesn't like his private information or photo being online, he relented enough to let me post a pic of the pair of us as my profile pic (but won't set it to his pic, which annoys me).

He also has it set so he has to approve all tags.

What should I do / say? I don't like this and it seems like a red flag.

My boyfriend has almost nothing "personal" on his Facebook, why does this bother me?
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