This is a forum it’s good as a forum.
It’s not a programming, versioning, collaboration platform.
Thinking that one platform should do everything and a company shouldn’t use better, third party tools is stupid.
As for professional companies should make sure their forums are also great programming collaboration platforms, here’s a few other companies that use github:
Google: https://github.com/google
Microsoft: https://github.com/Microsoft
Adobe: https://github.com/adobe
Twitter: https://github.com/twitter
Facebook: https://github.com/facebook
Some major programming languages that are actually published and maintained through Github:
Python: https://github.com/python
Typescript: https://github.com/Microsoft/TypeScript
php: https://github.com/php
Then there are all the platforms and other companies that use it. Of course, Git, having been written by Linus Torvalds (Linux creator), is also the location of the Linux Kernel:
Linux Kernal source: https://github.com/torvalds/linux
There are other great minds in computer science that publish there also.
Then of course, there are the major education institutes:
Stanford: https://github.com/sul-dlss
Oxford: https://github.com/ox-it
MIT: https://github.com/MITGameLab
And all the other major universities worldwide.
Don’t forget of course, major governments:
US Government: https://github.com/unitedstates
UK Government: https://github.com/alphagov
AU Government: https://github.com/govau
…just about every national government in the World:
https://government.github.com/community/
and government organisations and government funded bodies:
NASA: https://github.com/nasa
CERN: https://github.com/CERN
then of course, major platforms that could be listed here and lastly (though it would be easy to go on):
Deepmind (creators of AlphaGo): https://github.com/deepmind
Totally not a platform that professional organisations would use, despite having their own forums as well.