I'm a paying customer, so I like SourceHut a lot, but it's easy to see why it won't be nearly as big as GitHub.

* GitHub was much earlier

* GitHub was backed by venture capital, and is now backed by Microsoft

* GitHub doesn't force you to adopt an email-only workflow. Pull request are much maligned in tech circles (following Linus Torvald's rant), but people all over dev teams love them. They are a huge argument why companies don't just stand up a git repo and call it done, devs want all those workflows and issue trackers and stuff. SourceHut is very barebones even where it has them. (The exception would be build actions, where SourceHut has no real integrations into big tools, but the core build action system is superior to GitHub's, IMO).

Incidentally, the build system depends on qemu: https://drewdevault.com/2018/09/10/Getting-started-with-qemu...