I'm conflating them because, in my experience, they're not independent. There are, of course, plenty of exceptions, but those characteristics tend to go hand-in-hand.

It's also often the case that what superficially looks like "ugly reliable code" actually means code that was, at one point, very simple and tidy but has been battle-hardened by years of maintenance. It's ugly because code that implements a lot of complexity tends to look scary as hell.

Finally, it's ultimately a truism: truly unreadable code is also code that's hard to modify, and very few systems will go through their lifetime without changes. Even if it works fine today, it'll not meet business requirements tomorrow, and its unmaintainability is a liability.