As a programmer, you don't see obvious practical use in understanding results in number theory? These have importance in a wide variety of computer applications.

What about linear algebra? Do you really think that understanding its applications in computer graphics doesn't/wouldn't improve your employability?

Certainly, if you're a janitor, having studied philosophy vs. mathematics does not significantly affect how you do your job (though it probably does affect how easy it is for you to get a different job). But mathematics--even advanced mathematics--has more and more obvious applications than philosophy.