Some services run really good behind a reverse proxy on 443, but some others can really become an hassle… And sometimes just opening other ports would be easier than to try configuring everything to work through 443.
An example that comes to my mind is SSH, yeah you can use SSLH to forward requests coming from 443 to 22, but it’s so much easier to just leave 22 open…
Now, for SSH, if you have certificate authentication or a strong password, I think you can feel quite safe, but what about other random ports? What risks I’m exposing my server to if I open some of them when needed for a service? Is the effort of trying to pass everything through 443/80 worth it?
Imagine opening all the windows in your flat. Then leaving them open for a month. What would happen? How many insects would make their new home in your home? How many critters and cats would do the same?
Now, each window is a port. Your flat is your network. Each critter or cat is a bad actor. Each insect is a bot or virus.
This is an awful analogy…
To expand on this a bit:
A lot of attacks are automated since the goal is to compromise as many hosts as possible. These hosts are then used in a botnet or sold to people on shader websites to use as proxies.