I think that's the exact opposite reason why the genre is stale. SWTOR, Guild Wars 2, Neverwinter, and everything else post WoW has come out with polished leveling treadmills and endgames that range from bad to nonexistent.
The problem with the genera is that devs treat MMOs like they're RPGs. You play RPGs for a few months, beat them, and then forget about them. Some RPGs do have replay value, but how many people were playing Planescape or Baldur's Gate in 2008? But 10 years later WoW still has around 7 million subs, and EVE is still growing. MMOs need to have gameplay that's more like LoL, Starcraft, or Civilization. That's not to say they need to have the same mechanics, but elements like leveling and story are not as important as what happens at max level.
TBH, the solo leveling treadmill is the problem with MMOs. I'd pay $50/month for a game that was just group PVE, crafting, raids, and PVP.