Queues effectively occur if a server has reached its peak limit of concurrency, basically when the amount of players already logged in completely saturates the capacity limits of its hardware and databases. Or, to put it differently: the boat is full, adding more passengers will sink it.
Said limit cannot be increased beyond where it already is, hence the offer for a free migration elsewhere (where the limits haven’t been reached yet). Please have a look at the recent forum post by the producer of WoW Classic, which goes into a lot more detail on how things work and how our plans look like: https://us.forums.blizzard.com/en/wow/t/classic-the-unacceptable-state-of-classic-servers/1323722/7
Given this isn’t actually a topic relating to technical issues, I’ll however now close the thread.