My guess is that it's that these particular branches of physics and philosophy overlap considerably in the field of "what are the fundamentals of stuff". A biologist is interested in how organisms work, but is less interested in how the atoms making the organism came to be. A materials scientist is interested in how different things are tough/strong/flexible/tasty over the fundamental origin of those things. A social scientist is more interested in how humans interact with each other than how humans physically originated.