I think the real problem is we were sold all these complex processes that supposedly deliver better results, while in reality for most people and orgs it's just cargo culting, like with Kubernetes, for example. We can get rid of 90% of them and be just fine. You easily get away without any kind of CI in teams of less than 5-7 people I would argue - just have some sane rules and make everyone follow them (like run unit tests before submitting a PR).
Which is actually useful.
and thus you discover the value of CI
Good luck implementing merge queues yourself. As far as I know there are no maintained open source implementations of merge queues. It's definitely not as trivial as you claim.
Why? I know plenty of teams which are fine with repo and CI being separate tools as long as there is integration between the 2.
The whole PR and code review experience is much more important to me. Github is striving to set a high bar, but is also hilariously bad in some ways. Similarly the whole issue system is passable on Github, but doesn't really reach the state of the art of issue systems from 20 years ago
GitHub’s hosted runners support a grant total of two architectures.
The only forges which I’ve seen with more variety are distributios’ forges usually hosting their own runners.