Why does it seem that everything that I read in philosophy always uses "she" or "her" instead of "his" or "he"?

Although I try to use "he or she" or "she or he", and I do like "s/he" and even the allegedly ungrammatical "they" (though I read somewhere that it's not really ungrammatical), often the best solution is to rewrite the sentence to avoid the problem. The best advice on this appears on the American Philosophical Association's website: Warren, Virginia L. (2001), "Guidelines for Non-Sexist Use of Language" .