I would guess that since all the SE sites and their metas use the same software (I think...), it's just there by default, but it's set to display our rep from the parent site. Although, I only checked here and on Programmers; SO is different - it seems to have seperate reputations for SO and SO's meta (exampleexample - notice his meta rep and SO rep). Not sure why it's different here, though.
replaced http://meta.stackoverflow.com/ with https://meta.stackoverflow.com/