You still have AppArmor or whatever, it wasn’t really an OS specific tool or configuration process. To me it was more like - less bugs, because the dev was done on Ubuntu and so more got addressed. Less configuration, because they made sure to get the packages or kernel modules in upstream for an easy install for new devs, or it comes installed, as opposed to having to add a new repo and go get it. Less barriers, even if the barrier is just one extra command. These quality of life things that made it easy to do dev on Ubuntu, particularly for cloud native tooling right when everyone was shifting to those stacks, also made it easy for Ops teams to adopt it. More novice users who want low barrier to entry meant more StackOverflow answers available to troubleshoot it. Lots of intangibles that might strike a hardcore Sysadmin as irrelevant when choosing an OS but I think they made a strong difference.