Proprietary 'shell' vs. linux DIY/customized setup.
There are a multiple publically accessible/usable sources which can be found via search engine(s) to extend bash / unix shell functionality based on points discussed in topic link.
Those two "PowerShell"s are not the same. For the sake of cross platform deployment, they moved away from the original a lot -though they managed to support many things in time. The old and original one was released in 2006,IIRC, so it didn't exist in 90s.