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?
This is security theater
Flaws in SSH do happen but they are very rare. The solution to this is defense in depth which is different than security by obscurity.
My comment was not a recommendation. OP asked what the danger is of leaving short open on port 22.
Also, tools are not secure. Their implementations are secure.