Why? Because the government hates competition. Because every home schooled student means less federal money for the school district. Because less federal money for the school district means less money for teachers unions.
Did I leave anything out?
Homeschoolers and private schoolers are going to be the leaders of tomorrow. First, they're taught a more conservative lifestyle - plus they're getting a good education to back it all up.
Kids that are not in the public school also have no records that can be used against them later in life. Chicago type politics won't work on them.
Last, but not least, the more lives the public schools can destroy the more democrat voters there are. Unless they can get their hands on home schoolers and private schoolers, these kids are going to escape (and their numbers are growing rapidly).
Yes, the indoctrination to make all the children good little socialist drones.