The idea being that we could be more up to date. It would(to my friends who play Blizz servers) sell better to them to come be apart of our community and donate to help a private run of the more recent expansions. I realize the numbers don't lie. But the fact that we would be more up and coming. Also, seeing as no one(as far as I've seen) is running WoD, let alone Legion, we would be "on top of the game," per say, to people who don't want to sacrifice the feeling of the new content, but also don't want to HAVE to pay to play.
That's my defense. Granted, its based on the idea of being with the "in."