I would think that the better the code is designed and factored and refactored, the easier it is to maintain and evolve, detect and remove bugs and security vulnerabilties from it. The ease of maintenance helps both AI and humans.

There are limits to what even AI can do to code, within practical time-limits. Using AI also costs money. So, easier it is to maintain and evolve a piece of software, the cheaper it will be to the owners of that application.