Don't know if outdated is the right term. It was just not a success commercially. I have two of them and love them, but I long ago stocked up on brass and ammo.
All of the Super Short Mags, the 223WSSM, 243WSSM,. and 25WSSM, were introduced shortly before Winchester closed its New Haven manufacturing plant in 2006. No M70s were made until 2008 at the new plant in South Carolina, By that time the WSSMs were pretty much dead commercially.
Also there is/was the argument that they did nothing that existing cartridges wouldn't do.