It's important that the schools remind parents how difficult it is to teach kids because then parents will keep putting up with the crappy education their kids are getting in school—and parents will be grateful for it.
Family schedules take second-seat behind the school schedule. If the school decides kids need more school days and less summer vacation, families comply. If a snow day means school goes longer in the summer, families comply.
Schools offer free babysitting, but every once-in-a-while, they make the kids stay home and since parents are not set up for it, parents feel that they cannot cope with kids at home.
The education stuff is so easy compared to everything else, but the education stuff is what scares everyone from homeschooling. It's so clear, once you are homeschooling, that this is true, but so hard to see until you take on the education yourself.
The school system has to constantly sell to the parents that teaching is too hard for parents. One of the ways school does this is tell you that national math curriculum is more important than playing in the snow. Because the teachers create a curriculum that caters to a classroom, and they downplay the value of things that cannot be done in a classroom. There are a million examples like this that add up to the schools telling parents they are incompetent.
When parents consider homeschooling and they think they won't be good at it, that they aren't capable of educating their kids as well as the school, that's when school has won.