I mean to each their own, but in my own experience, I value being able to easily and reliably copy-and-paste code snippets across projects (and I have a million of them, across several evolutions of my own personal coding styles and conventions) or files without worrying about whether the typedefs are in scope, polluting a namespace with possibly conflicting names or macros, etc.

I also have often found myself publishing “for my own use only” code as open source later and like to keep things understandable to maybe help teach someone something someday.