I obviously don't "know it". But I can say it's something I've witnessed a number of times.

It may be due to the fact that I live in Idaho which has extremely lax standards for homeschooling (which is why some of the cases I observed happened, people fleeing other states so they could avoid oversight on their kids education).

I will admit this is mostly just my own anecdotes. But, it's also the reasons given by a number of my family members and people from my former church that go down that route.