Earlier quoted context omitted.
I'd be interested to hear why. I have no problem with companies choosing not to open source in the first place, it is just the idea of taking an open source project with an active community around it and closing it up that is a tough pill to swallow.
I won't get into all the context, but I think we should consider whether a community without contributors is a community. GL JS never had major active contributors outside of the company, and there are no self-funded webgl experts with lots of time who are ready to maintain a fork. OSS, we hoped, was about enabling people and unlocking people's ability to collaborate. It turns out that in 2020, it's mostly helping co…
But there's more to it. When the roadmap of an open-source project is tightly controlled by a sponsor, that can make third-party contributions hard or impossible. I know OSRM much better than MBGL so I'll cite an example from that - the distance matrix issue. This is massive for many users, plays right to OSRM's strengths, but Mapbox wouldn't accept patches to provide it for _years_. IIRC it only got in when Mapbox's attention shifted to Valhalla.
I'm not blaming the Mapbox devs at all for that; it wasn't important for Mapbox's business, and any extra code inevitably brings a maintenance burden. But it partly explains why third-party contributors are reluctant to contribute when the roadmap's out of their control.
Back on MBGL, there was/is a community, but the community formed around MVT rather than MBGL specifically - again, possibly because MBGL is just so good. https://github.com/mapbox/awesome-vector-tiles sums up the enormous community energy in the space (I think that might be your document originally, apologies if not). It's kind of a shame that MBGL being so far ahead of everything else has probably crimped development on alternative renderers.