For to translate man back into nature; to master the many vain and fanciful interpretations and secondary meanings which have been hitherto scribbled and daubed over that eternal basic text homo natura; to confront man henceforth with man in the way in which, hardened by the discipline of science, man today confronts the rest of nature, with dauntless Oedipus eyes and stopped-up Odysseus ears, deaf to the siren songs of old metaphysical bird-catchers who have all too long been piping to him ‘you are more! you are higher! you are of a different origin!’ - that may be a strange and extravagant task but it is a task—who would deny that? Why did we choose it, this extravagant task? Or, to ask the question differently; ‘why knowledge at all?’ - Everyone will ask us about that. And we, thus pressed, we who have asked ourselves that same question a hundred times, we have found and can find no better answer...
Friedrich Nietzsche
Because it’s really really useful?
Jeez, people really don’t appreciate poetic language around here, huh?
(That would probably be close to my answer too, I’m just a little stunned by all the downvotes.)