The 7mm WSM might even be the best of the bunch, but it fell into a vast field over-populated with 7s. I never really had a chance, from a market success point of view.
I often hear people say that the 284 class is over-populated, but realistically you're only going to find two 7mm options at most stores, the other 7mm's are pretty obscure by most people's standards. I think the issue with the 284 class is more that you have a hard time convincing people to buy something other than a 7mm-08 or Rem Mag and that's hard to do with slow twists and lighter bullets.