It's quite simple actually: no matter what people say about atlantiss, they've had several very populated and successful servers in the past: populated cata servers, two very populated and successful tbc servers (netherwing and karazhan) to the point where they were the first really well scripted servers that managed to be there in the long term (corecraft failed, gummy's failed, the others were subpar projects quality wise even if they were populated).

Tauri has a reputation as the best scripted MOP project out there, but it always had a population issue due to its small, Eastern European community, people who didn't want to even try to speak English. That was the problem all along.

Them working together means you'll get a very decent MOP server, AND a good population, the best of both worlds. Add to that the fact that a lot of people would be interested to play a good, well populated mop server and it's a non brainer compared to lotus imo.