During the industrial age, when parents moved from farms to factories, it became more cost-effective to put kids in school than put them to work. So parents bought into the idea of state-run school. At that point, school became the most expensive babysitting operation on the planet.
In the pre-industrialized world, only the kids with a governess got an education. And those governess types were so quirky and fun because it was an alternative choice to be a governess instead of stay in the town you were born in, get married and have kids of your own. (Think of going airborne with Mary Poppins, or singing with the von Trapp kids and Maria.)
In today's school system teachers choose teaching because it's safe and predictable. You can generally get a job teaching where you were born, and (before Scott Walker busted unions) teachers could rely on a lifetime position.
The problem is that today's workplace rewards risk takers. It rewards entrepreneurial thinking and people who are trained to think independently and creatively – information synthesizers. Why is it good to have people who took a safe route training people for an inherently unstable workforce?
The parents most willing to stay home and teach their kids all day long are probably the parents who do not fit in well in corporate America. That's why they are willing to leave and stay with kids.
What if we had only the workplace geniuses running homeschooling? Would that be better? Are we aiming to train our kids so that they can successfully navigate the workplace that dominates adult life instead of leaving the workforce? What is the best type of person to teach children given the world they will need to navigate?