How do they find me?

So I've had a resume up on a webserver that holds a bunch of files for me but that has no index.html file so you can just grab those files if you wanted to. I know its not very secure but if you're really dying to steal my spanish essays, be my guest. They suck anyway. So despite the fact that there was not (until now) a specific link to that resume file, two different people have googled me and asked me to tutor their kids. My resume's not even designed around the fact that I've done some tutoring, it just happens to be there and for whatever reason, it seems to be doing me quite well just sitting there inconspicuously. I love this. So if people find me even when I don't advertise, why do so many people spend so much money advertising?