It is useful to put homeschool in a somewhat historical perspective. Because of the pervasiveness of public and institutional education over the past 100 years or so, it is easy to think that this way of educating children is the way it has always been done and that it is the best system possible. However, the development of public education into the monolithic system that it has become is a relatively recent turn of events when viewed in an historical context.
In the ancient times, societies in which education was valued, for example in ancient Greece, most education was done through tutoring and other very focused avenues. As time passed and institutions starting providing education, these institutions tended be religiously based and were largely independent of any large organization. This was mostly the situation in the earliest American communities; most colleges that were started in that period were actually founded for religious purposes.
In the 1700s through the 1880s, schools were often established by and for local communities. These schools were funded and controlled by the local communities and usually consisted of a single teacher and a single schoolroom. The amount of time children spent in school was fairly limited in both the number of days they attended and the hours of instruction per day that they received. Because these schools were based in and controlled by people in the local community, they answered directly to the people whose children were being taught. In the times when children weren't attending school, parents often taught them at home or they learned independently.
Eventually, the system of locally operated and controlled schools evolved into larger and larger networks of schools forming school districts and corporations. State governments began to take more control of the school systems and the federal government began to get involved. As school systems increased in size, including the inherent growth in state and federal bureaucracy, the ability of parents to have a significant influence over how their children are taught diminished.
By the 1970s, governments and other large bureaucratic organizations, including the teachers' union, had mostly taken control over schools and local participants actually had very little say over what occurred in those schools. This "evolution" (or devolution depending on your point of view) continues today. The policies and practices of school systems today are largely determined by state and federal policies and programs. Parents have little say in how schools are actually run. Their primary influence over school systems is indirect through school board elections, but even these school boards are typically limited in their authority to manage the schools.
The decline in what many consider to be the general levels of societal accountability and responsibility has fed the decline in the educational system and vice-versa. Because the education system doesn't prepare children adequately, on many levels, society in general experiences a decline.
Actually, the homeschool movement drives the responsibility for education back to the parents, those with whom it originally belonged. As more people embrace the opportunity to provide the best possible education for their children, the number of homeschooling families will continue to increase.