There were several issues with the 223WSSM and the 243WSSM. One already mentioned, the cartridge was short and fat with a sharp shoulder, which can cause feeding issues. Another was barrel erosion: Browning and Winchester had to chrome line the bores on the rifles, and even then the bore erosion was extreme. And neither really offered any more than shooters could already get from other cartridges that were already available. The 223WSSM did not really do a whole lot more than the 224 Middlestead or 224 TTH wildcats, except it had a lot more bore erosion. The 243WSSM offered little improvement over a 243 AI or 6mmAI, and the barrel life issue was a major setback for Browning and Winchester. I think most shooters are seeking some kind of balance between accuracy, velocity, and barrel life, and the WSSM cartridges did not offer it.
Also, Winchester got sued by the developer of the WSM cartridges, and dropping the WSSM line may have had something to do with that.