There are at least a few different "OSS scenes" that have different priorities. More principled, idealistic developers fall under a different category than more pragmatic ones, so it should be no surprise that they use different tools.

Using non-Free tools has been shown to be distinctly non-pragmatic under a wide variety of considerations.

A better term would be something like "Tied programmers" or "Dependent progammers". Maybe "sharecropper progammers"?

"Sharecropper programmers" might be an accurate way of describing developers for Apple platforms, but that's not what is happening when people use GitHub and Discord to work on open-source software. They can easily move their Git hosting and chat to another platform—they just choose to use the popular, coincidentally non-OSS, platform for its pragmatism.

A large base of existing users, easy onboarding, and good visibility makes a big difference for many OSS projects. Using a self-hosted Git hosting system and mailing list is a lot of work—and it adds a not-insignificant barrier to entry for potential contributors. What issues exist with popular, proprietary Git and chat tools that make them unsuitable for OSS development?

What are some of the considerations you're thinking of where using a popular option is not pragmatic?