Agreed. I hope https://sr.ht can help resisting this trend. I'm sure there are plenty of happy Git(Lab/Hub) users here but again, I'm not convinced these platforms would fit Org's needs.
For me pull request model is much more natural than mailing lists and patches. It doesn't matter at all if its GitHub, GitLab or (my personal preference as it's lightweight, open source and easy to use) Gitea (interestingly it's not present in comparison on https://forgeperf.org). I don't even know how to make PR on sourcehut and can't find any tutorial.
Of course I will try to learn in order to help org but the entry barrier is much higher than for Git(Lab/Hub/ea).
EDIT: I just found orgmode code on Gogs here: https://code.orgmode.org/bzg/org-mode
That's great! I'll register and try to help soon! Mabye it should be more visible and linked in docs (I'll... make a PR I suppose? :)
Rather than attaching a patch, you simply send a link to your git repository (+branch if applicable), and the maintainer can pull from it.
But please clone Org's repo, make a patch - perhaps with https://magit.vc - and attach it to an email you send to emacs-orgmode@gnu.org: that's all it takes.
Then we will help with polishing your contribution :)
For those who are really taking advantage of org-agenda et al, I'd argue GitHub issue tracking UI is far more restrictive for tracking patches.
If I were in that position I'd be duplicating issues into org-mode anyway (or using an Emacs mode to interact with/sync them). Maybe that's the missing link?