tl;dr "we had our vLLM fork and it's unmaintainable now; guess we are going to rebuild it, in the public this time"
Unmaintainable seems unduly harsh. There is a big gap between maintainable internally and ready for public consumption
If you are in the same boat you'll see how much changed in vLLM compared to one year ago. Also, this meant that they haven't rebased for over a year, I don't believe that's because they don't want, it's because they effectively can't.
Yeah, surely they can maintain it as-is. But it will be increasingly hard to port over anything community has.