'Natural Philosophy' was a useful term before we began to develop ways to actually study the physical world and catalog the results of experiments. But demonstrably different concerns need different nomenclature for reference. As 'religion' was gradually reduced to a specific concern, science & philosophy sort of automatically became distinct concerns also... with philosophy settling into a study of "how to think" and how to think about the other realms.
I was a philosophy major for 2 years before I worked out an answer to folks who asked me 'why' & 'what' it was all about. I finally hit on: "It's an excuse to meddle in everyone's business." Just put "Philosophy of *****" in front, and you can expound on almost anything.