Why have hangars not been opened to invite friends in?
TL;DRHangar invites weren't possible because hangars ran locally; moving them to the game servers in 2.4 makes it possible to start working on inviting friends, and it will come.
Because that relies on persistence. Because the hangars up to this point have worked entirely on your local computer. And part of what happens in 2.4 is we move the hangar up to running on our game servers. After that, we can start working on bringing people into your hangars. Plus, with the addition of ArcCorp and Crusader, it became less urgent to invite to hangars because everybody pretty much had the same hangar. Everything was in the same place, a couple different ships and whatnot, but for the most part, it's the same thing. Now with 2.4 and persistence and your ability to arrange your hangar how you want, your hangar will start to have its own personality. Then it becomes worth it to take the time to start inviting people to hangars. So it'll come. It just hasn't been possible up until now. And now that it's starting to be possible, we can start working on it.