Like Michael, I haven't seen it. However, for me, it means a lack of attractive, available men. You could say a bar with too many women or men you don't find attractive has a 'major lack of male real estate'. It's a jokey way to express it.

As a disclaimer, I haven't actually watched any Vampire Diaries, but when I hear "major lack of male real estate" the first thing that comes to mind is having a small penis. I think that TRL is this: https://en.wikipedia.org/wiki/Total_Request_Live