Sometimes it happens that there aren't any players up that would have a 3+ connection with you, especially if one is from Europe. That, and people are scared from receiving a beatdown, usually people in ranked refuse to fight with you because of that.
Thats the whole point of the rank filters though, granted the connection thing doesn't really work well. I have mine set to only finding people with a 4 bar connection but when i find people sometimes it shows they only have a 3 or lower connection with me. As for lobbies i don't get it at all. why so many flat out disperse when i enter makes me think i have some reputation lol