Private schools offer an alternative to government education. Limitations exist, however, and foremost among them is the sometimes prohibitive cost of tuition. So while private schools may have superior teachers, more rigorous standards and a safer environment than their government school counterparts, the model is similar. Well, but perhaps it's the only choice for parents who need to work outside the home.
So the real reason is revealed -- it's "free"(except to us taxpayers) babysitting!