Single-vendor is not proprietary because I can fork VSCode and I can't fork Microsoft Word. Single-vendor open source is the balance some companies have found between sharing their software with the community and capturing the value of their employees' labor. It's less free than openly developed FOSS and more free than proprietary software. It's unrealistic to expect all software to be openly developed FOSS with toda…
Well, sort of. You lose a whole bunch of stuff (e.g., Pylance) by doing so.