Hi Peter. Sorry for the slow reply here.
There are a number of advantages GitLab gives for documentation in specific.
Pagure allows rudimentary web-based editing, but it’s just presenting a basic web browser form. This can be really frustrating (not theoretical — I’ve gotten that feedback from users). GitLab has what it calls a “WebIDE”. There is even work in progress for that to support AsciiDoc previews. Although long-term docs-teams writers will probably prefer a local checkout, this is essential for drive-through contributions — and really, contributions from anyone for whom git is an intimidating barrier.
GitLab also has a much more rich user interface for reviewing proposed changes — “Merge Requests” instead of “Pull Requests” in their parlance. Rather than disconnected comments, individual comments can be grouped into a coherent review, and that review can be updated. And, as part of that discussion, parts of the conversation can be marked resolved individually — making it much easier to work through a big change.
Plus, the Merge UI itself is just a lot friendlier.
I think using Pagure presents a technical barrier to contribution for a lot of potential writers. These two things are big in my eyes, but there are lots of others as well. (For example, the ability to gate a merge request on an external confirmation.) I wish Pagure was at the same level, but we just don’t have the requisite developer base to even close to keep up. See Issues - pagure - Pagure.io and https://pagure.io/pagure/pull-requests for just the backlog — and note how few have been actually resolved in recent times.
I’ve written about this before: I wish GitLab would abandon the “open core” model and make the whole thing open source. I think we have a greater chance of influencing them to make that happen by working with them rather than not. Making a git-forge isn’t the Fedora mission, and if I did suddenly get an influx of engineers, I’d really rather them work on things that make Fedora infrastructure better, or improve Fedora Server itself.
I hope you can accept this compromise. We can also look at making ways for people who don’t want to use gitlab to contribute. That would be more complicated, but fundamentally it’s git, so I’m sure we could figure something out.
On the privacy issue in particular: I also share that concern, but personally I think their privacy policy is reasonable: they respect Do Not Track, and there’s also a central opt out (not one per service or page or whatever), and they conform to applicable global privacy laws.