because deployment via Docker is cumbersome and annoying IMO, Docker
containers are notoriously unsafe (especially when run by the root user
which is the default), hard to isolate network-wise and offer no real
advantage here. Deploying xymon in a secure way (with encryption via
stunnel for example) takes time and lots of configuration entries, I
really don't see how putting the server component into a container would
make things better.

[Scot Kreienkamp]
Why would deployment via Docker be any more cumbersome than doing an install from tarball?  Or from RPM install for that matter?  I’m running dozens of containers in multiple places.  I prefer running containers over direct installs.  The advantage is in the ease of install, ease of upgrades, not having to manage dependencies and conflicts, and that absolutely everything it needs to run is already included in the packaging except your config.  I've done stunnel, that could also be added into the image as a default at another port, in which case it would already be available as a default config for those wishing to use it or who don't know how, or it could be done outside the config by an admin.  If I made a docker container of the current version of Xymon compiled on RH9, someone could immediately run that on RH10.  Or Debian, Ubuntu, Rocky, etc.  How is all this not an advantage? 

On the security side, I agree with you.  There's no real advantage there inherent to using a docker image for Xymon.  It's not possible for it to be more secure because then it couldn't do its job.  But that doesn't detract from all the other advantages that containerization would bring.