I can imagine lots of reasons. To build on PowerShell means either integrating your changes upstream (not likely, given fixing some of the clunkiness would requ

I can imagine lots of reasons. To build on PowerShell means either integrating your changes upstream (not likely, given fixing some of the clunkiness would require breaking changes) or maintaining a separate fork and incorporating patches from upstream constantly (a lot of work, and constant conflicts aren't fun). Plus the fact that PowerShell is .NET-based and not the most snappy shell out there either. Plus the fact that extending something requires investing a lot of work just understanding how things tie together, and then avoiding messing up all the hacks and idiosyncrasies added along the way instead of having a clean slate to build on.