The worst-written software always lives the longest. Maintainable, modular software, by definition, is easy to change and swap out. So the evolutionary forces favor awful spaghetti codebases that everyone is too afraid to touch.

So then the solution would be true natural selection and self-evolving software. As long as external entities (programmers) are tasked with killing off the unfit code, selection is going to be pretty bad.

Nah, they weren't buggy, it was just user error. Nobody stepped on them properly.