That would be good. Until then we can only speculate as to their exact motivations.
I still think it is wrong for the government to have any say about whether parents educate their children or not, much less how they educate them.
It's a Catch 22. If the schools don't maintain standards, then people complain that the public schools are cesspools and nobody is learning anything. If they have a requirement like this, some people will complain it's an infraction on the rights of parents.
I personally think the public schools are only responsible for the basic skills to be a good citizen, get a job, and function in society. Parents should have to demonstrate their students have achieved this much, so the children are prepared to function in the adult world.
In these cases, though, more should be required. I don't know if this came up on the thread. These home study students who keep up with an approved plan graduate with their classes and have a public school diploma from that local school. So, of course there have to be some assurances that the student isn't being given a gift, sitting home and not up to the same level as students in school.
The alternatives? Private schools, GEDs, and Junior/Senior year in a public college.