My understanding is that pylance bundles in several ML models that back a lot of its performance increases over pyright and it is the ML models and closed-source data science that caused the LSP closure.

I think data science also is best when it itself is open/open-source, and peer reviewed.

I can understand why Microsoft wants to make that a moat to protect expensive data science and ML research boundaries and it doesn't seem that baffling to me if that is indeed the reason why they closed source pylance, even as I question if it was the best choice.