The reason is largely historical [1]. Before about 100 or so years ago, almost every serious scientist or mathematician was effectively a philosopher as well (hence the Ph in PhD). Aristotle was (and still is, albeit augmented with more modern interpretations) foundational to almost every scholastic curriculum. "Philosophy" literally means "the study of knowledge", and for much of human history, it has been where big ideas came from.
Philosophy gave us many of the things we consider science: the scientific method is the direct result of many of the enlightenment philosophers' quest to determine "what is real" versus "what is not real". Once you have an agreed upon, repeatable definition of a process to get to "real", you can move on from there.
Once the total knowledge of our species began to expand toward the middle of the 19th century, it was no longer sufficient for a scholar to be a "philosopher". You had to specialize in something. So philosophy became dominated by the left-over "soft" topics like ethics and personal philosophy, leaving many people working in "hard" disciplines to shun the label of "philosopher".
Interestingly enough, the classification problem is still one of the most hotly debated problems in philosophy. How much of our classification comes from a truly singular concept versus linguistic commonality? I don't have the answer, but we've been asking the question for a long time.
Philosophy gave us many of the things we consider science: the scientific method is the direct result of many of the enlightenment philosophers' quest to determine "what is real" versus "what is not real". Once you have an agreed upon, repeatable definition of a process to get to "real", you can move on from there.
Once the total knowledge of our species began to expand toward the middle of the 19th century, it was no longer sufficient for a scholar to be a "philosopher". You had to specialize in something. So philosophy became dominated by the left-over "soft" topics like ethics and personal philosophy, leaving many people working in "hard" disciplines to shun the label of "philosopher".
Interestingly enough, the classification problem is still one of the most hotly debated problems in philosophy. How much of our classification comes from a truly singular concept versus linguistic commonality? I don't have the answer, but we've been asking the question for a long time.
[1] http://en.wikipedia.org/wiki/Doctor_of_Philosophy#History