This servers aren’t currently capable to handle a large load of players. They had to do two restarts today. I doubt that they will invite many people to the beta. Elwynn Forest crashed today and a bunch of lagging issues. This is why they couldn’t flood all of you in. They want to actually test the game and the bugs, not spend 2 weeks maintaining server stability.
Restarts are controlled updates. They’re applying patch fixes in real time.