It's not. SSL in itself doesn't make any exposed service safe, just safer. An updated service isn't necessarilu free of vulnerabilities.
The difference between exposing your login page and most other services is the attack surface. If someone gets into your NAS administration, game over. You're getting hit with ransomware or worse.
If someone gets into my Calibre Web server, for instance, my vulnerability is much more limited. That runs in a docker container that only has access to the resources and folders is absolutely needs. The paths to doing harm to anything besides my ebook library are limited.
I of course still use SSL, with my Calibre Wev behind a reverse proxy, with long complex passwords, and I'll probably soon move it to an OATH login where I can use MFA (since it doesn't support it natively itself). And there are more measures I could take beyond that, if I chose.