Probably Atlassian was sick of people never upgrading their old installations and getting hacked for it, and people did not upgrade because it is quite a hassle in the first place, not to mention plugins breaking allll the time.
Oh and because cloud forces continuous payment whereas prior many customers simply bought a one year license and went on without renewing support.
We're running a selfhosted Gitlab Premium since 2019. The only two times in the last 3 years we had issues with artifacts not being deleted (causing nightly backups to become 500gb, will be fixed in the next version) and some out of date apt certs to run "apt update". Otherwise, I update Gitlab every month without problems.
Gitlab is a breeze to upgrade when using the Docker distribution. Swap the version number in Kubernetes or the systemd unit file (if you're using naked Docker), restart the service, that's it...
Atlassian's docker images are similarly easy to use, but with everything Atlassian you have a veritable ecosystem of plugins of which almost none are open source so you are out of luck if there are incompatibilities.
I've had experiences where devops minded people I've worked with have wanted to self-host services such as Bitwarden. Sure, it will be cheaper and you will have noone to blame but yourself, but once things go bad they go really bad. It's also another thing to keep eyes on.
I guess similar argument could also be extended to self-hosted clouds. Seems like it could take away a lot of focus and energy from working on the product itself.
No. You update it on patch day (or when a big CVE comes out that you are actually impacted by) and know exactly what goes wrong and when. If you can't solve it, you roll back. When Github (or a part of it) goes down, you know nothing and with persistent issues there's no way to solve it either.
A company of the size where "but we have to scale" is an actual issue should self-host. A SaaS solution is a risk that you cannot mitigate.
A lot of large web services outages (such as GitHub, Azure Active Directory, Slack, etc) are purely caused by these services having to scale to the entire world, with all the complexity and moving parts it entails.
Self-hosting inherently mitigates that problem because you now need to support less than 0.1% of the load of the worldwide service.
It also puts you in control of maintenance and updates - you can choose to make changes outside of business hours so that nobody is affected if you screw up. Developers at SaaS services can't easily do that because it's always business hours in some parts of the world, and may not be motivated to do it anyway even if it was possible with some effort.