Lack of activity in Cata isn't warmane's fault at all, trust me. Over a years, wow players have this some kind of illusion in their mind, which was imposed to them by "hardcore", "challenge" players who likes to pretend that everything about the game before Cataclysm was so much better and more challenging, but unfortunately its just their nostalgia about good old times that they can't relive anymore. Cataclysm was the best thing that ever happened with World of Warcraft. World re-design, *****ic quest system was changed, and more great stuff added, which im kinda lazy to list. What you see about Cata being unpopulated expansion and being most hated (besides WOD) is unconscious social brainwashing.
Btw, i hope Warmane will make Legion server, that **** was unironically good tbh.