Nothing killed the workstation market. It's still totally a thing. Lenovo, Dell, HP, Apple ... all of these companies will quite happily sell you a dual CPU machine with masses of cores, oodles of ECC RAM, extremely high performance graphics with certified driver support etc.

All that's changed is that the architectures for workstations and "business class" desktop machines have converged, and the distinctive operating systems that were needed to support those older workstation architectures have gone away.