Mkmf and other core classes and Logger

While nosing around the code to the mkmf library due to another problem
I’m having, I noticed it has it’s own logging facility. I wondered why
it doesn’t use Logger since Logger is a core class too?

It would be useful to me while I’m debugging this other stuff to pass in
my own Logger instance, and I’m also wondering if other core classes do
this kind of thing and what would be the reason?

Just in case anyone knows.