My reason is that Ubuntu is relatively low maintenance and the packages in the ecosystem usually just work. On some other OSs, not everything works as smooth, so you have to compile stuff from source sometimes and tweak programs. You don't need to do any of that with Ubuntu and you can still run Kernel Virtual Machines (KVMs) of other Linux Distros.
I also use Ubuntu Server (20.04 LTS) on Azure quite often, it is able to provide security and stability while using relatively modern packages.
This has been ported from a reply on discord from myself to an article. Please feel free to comment and discuss this topic.