$$ has some play in it. Very few people just put up a server just out of the kindness of their hearts for nostalgia vanilla wow. Sure, that may be the initial goal, but thinking later on, these guys must have lives. They can't commit all of their life to this project without some sort of revenue stream. And why share this revenue with another server?
Also, both projects are hosted in different countries. Sure there can be collaboration if they wanted to cooperate, but it's harder.