With a VPN there's no need to change the port. Unless you change all of your ssh ports to another set pretty across all of your hosts, you're just asking for a headache at scale.

I wouldn't open up 22 to the world. I would change the port at a minimum or use a VPN.

This is like asking why no speaks one language saying, " I don't understand how/why people speak different languages."

Tons of reasons, some geographical, some political to some biblical, and other just out of spite.

To answer your statement... Tons of reasons; some listed already but too many to state. I suggest you research more and it'll help you understand why.

VMware on one, runs Ubuntu (and then docker) and various appliances. Xpenology on the other. Xpenology also runs Docker for more OOTB containerized apps.

I self host Mailu and don't have issues with it being blocked... If it's configured correctly you won't have issues.

I've thought about creating a blog on how to build it but haven't. Any interest in this?

I really enjoy Joplin