1. Consider if Windows did not come with any browser whatsoever. How would you get chrome? (or whatever browser you prefer... I realize there are ways, but for the average user, how would they get a browser?)
2. If I remember the percentage in this thread correctly of being 5% usage, that's still around the population of the United States! (Considering world population +/- non computer users). That's enough user data to sell and make profit off of to justify development for.
3. It does have it's uses. I use a few different browsers. Chrome variants, but schooling websites (although done now) always worked best in IE as some companies developed against the IE platform. For some reason, educational institutions were among them.