I switched a workstation to Secureblue for the very specific security priorities targeted by that project, but I think for the majority of users, the main reason for not switching to atomic is one you mentioned: why fix what isn't broken? The main selling point promoted to potential new users seems to be that updates don't break anything, but I can't remember a single time since Debian Sarge that an update broke anything for me, and I actually find the rpm-ostree package layering and updating process to be far more of a headache than otherwise.
Unless it's prepackaged like a steam deck, moving from the traditional way of doing things to atomic is a major change. Like any major change, people need a good reason to make it, and I think right now the only compelling ones are either hyper-specific (switching to okd and needing to build it on coreos, wanting to move to a specific atomic project, etc.), or just general curiosity.