a game launch has everything prepared and tested before and its just an early access but its basically just a staggered launch. this isn't a staggered launch this is a beta. they can make 8 billion server but because its untested there could be a flaw in each server that causes a complete shut down on systems
they need to test things out before people come in. they start out small like many betas and as more people get in the fasters beta invites go out. more people= more people possibly able to break and report things to help the game improve and free up more space and less time to fix each bug because they don't have to fix bugs on 1000 realms just a small number at first.
farther along beta goes less bugs so more servers can be open