Sounds like you were just doing it wrong
Either you run npm install from Windows if you are operating on the Windows file system or you run it on WSL if you are operating on the WSL file system both cases will be very fast
Or, as they said, they didn't want to have to think about it so they chose to switch.
The entire Windows operating system is doing it wrong. Seriously who daily drives windows these days. lol.
My memory is murky here, but I don't think WSL even had two different file systems at the time.