There are dozens of reasons we homeschool.
One reason is detailed in this article: http://www.deseretnews.com/article/765552031/The-war-on-boys-young-men-are-facing-a-new-crisis.html?pg=1
Education is now set up for girls. Teaching in classrooms, social learning, expected achievements based on developmental levels, college entrance, textbooks, and so many other aspects of public education are slanted toward helping girls succeed.
I have a lot of boys and only one girl. I want them all to succeed. I don't see any reason to put my boys at a disadvantage simply because they have a Y chromosome. I can tailor our education here for each student to succeed, so that the boys get the kind of education that helps boys learn. I can also ensure the expectations are high enough for them--that nobody just expects they'll fail/misbehave/whatever simply because they are boys.