Pylance started as open source and moved to a closed source model. Relevant discussion is at [0].

Then, they closed the .NET ecosystem [1]. This is a bit more complex and convoluted. Closed source debuggers, changing plug-in licenses, removing nice features from open source .NET runtime, etc.

So, classic Microsoft.

[0]: https://news.ycombinator.com/item?id=31763107

[1]: https://isdotnetopen.com/