Ducklingator

From what I've experienced, if it's without explanation they're usually either not looking for more members or didn't think you'd be fit for the position. Although usually the latter, I would just message the team lead and ask politely for an explanation. Most will tell you!

Some people are uncomfortable doing that. Yes, when you're the one who receives that message, you won't see anything wrong; but when you're sending said message, it's very uncomfortable to do that. You don't want to seem clingy, or bitter, or bother them, or whatever it is. Saying something like "The current members of our team are a sufficient assembly" or "Your application does not fit our standards" won't hurt anybody's feelings, trust me. 

When I was staff, there were votes for every single app to decide whether they'd be GM or not. If you're not GM (and they still do this) it means you didn't really catch anybody's eye.

Maybe all the shitposting was a factor