I didn't say it was an absolute. But once a scope grows to the point where you have to navigate to absorb a function or a loop, both readability and complexity tends to worsen. As does your mental processing time. Especially for people who "scan" code rapidly rather than reading it.

The slower "readers" will probably not mind as much.

This is why things like function size is usually part of coding standards at a company or on a project. (Look at Google, Linux etc)