Most of the thriving non-GPL OSS projects are supported and funded by large corporate sponsors--not by communities or foundations (e.g. React.js by Facebook, Blink by Chrome).

Furthermore, many non-GPL OSS projects have eventually gone proprietary (e.g. MongoDB's switch from AGPL to SSPL).

I think this gets the cause and effect backwards. No corporate lawyer prefers the GPL, so when companies start new open source projects, they don’t pick the GPL. Once a project has been started, GPLing it doesn’t really make it any easier to get it non-corporate support.

> Furthermore, many non-GPL OSS projects have eventually gone proprietary

Every time it happens people are upset and then forget everything a day later. To me non-GPL + corporate involved is a huge flag, especially if it's a more complex or niche project that'd be difficult to fork.

Are the thriving GPL’d projects not also sponsored by corporations - who fund the foundations and whose employees contribute the most code?

Those GPL'd(eg. GCC, Linux) projects predate their current corporate sponsors. The sponsors may go away anytime if they feel the project won't add any business value for them. I highly suspect if they would sponsor support any new GPL project.

Linux? Python?

But the direction of Linux as a GPL project is largely controlled by corporations e.g. Redhat now a.k.a. IBM, Intel, etc. GPL is not a cure all, it is a tool. Some licenses are better for some purposes. Use the right tool for the right job. It is nice that we have compilers (and OSes) under both licenses, it shows both strengths and weaknesses of each type of license. There are strengths, and weaknesses, to both models, and to other models, such as Intel's optimizing compiler.

The gpl projects are also corporately sponsored, just indirectly.

I would not call that "indirectly":

https://www.linuxfoundation.org/membership/members/

and that:

https://www.linuxfoundation.org/blog/2016/08/the-top-10-deve...

A fair amount of GPL work is done by researchers in public universities

The same is true of non-gpl work.

Half the linux foundation's funding comes from 6 companies. Not to mention the full time employees paid to work on it. And I find that there's similar patterns in a lot of other widely used gpl software. Similarly, MIT/Apache software gets tons of contributions from non-corp people too.