Church, sunday school, youth group, scouts, little league, 4H...
They are just jealous because homeschoolers do not have to pick their kids up at school and run them through a drive-through for dinner in order to rush them to these activities. The homeschoolers get to have wholesome, home-cooked meals (that the kids get to learn how to cook too!) and eat and relax as a family before going to AS MANY of those activities that involved SOCIAL INTERACTION with others as they want.
I guess they think that because schools are actually prisons, and children are required to stay there every day, that home-school is also a prison, and you have to stay home every day.