It's because several people pay sojs to get the game. So when mrllama started to stream, most likely the people who paid sojs had games, but some probably didn't.
Because IPs can fill up, it gives less chances for you to find a game. So those people want to keep searching.
Also, the stream is to get viewers and they get paid for that, so the longer you look the longer they get viewers and paid. The way of the world now. Yes it's a "service to us" but it's using us to gain as well.
As for the IP that has already walked? Well, them not telling you is just a guess. It doesn't matter if you know afterwards. I personally did not get his ip.
So I couldn't tell you either.
Knowing the IP afterwards doesn't do you any good anyways, as any pub game that is up, if you were to join it would say Diablo walks the earth so you wouldn't have to even check.
So it's really pointless to even know the IP afterwards.