When daily life already feels quite chaotic for some reason (like a new baby, or some other life event that stirs up the routine), then a relaxed form of homeschooling can feel like surrendering to the chaos. So a mom has an intense desire to keep order in SOME area, and academics DO lend itself to orderly progression.
I go through workbook periods when I just want to sit my kids down at the table, have them work and produce nice neat little pages of standard academics, without Any Trouble To ME. If I look back at when I felt this desire most, it's usually when I've gotten just past a major life event. I have enough energy to take charge a little but not enough to cope with too much new input. Unschooling feels threatening because it is open-ended and unpredictable, then; it seems to require more personal resources than I have.
We have had some real successes with our unschooling "sabbatical" this fall. I wanted to mention that because every time I post I seem to be expressing my concerns and anxiety. But there have been so many GOOD times.
I think the most significant successes have been with ME. It's kind of difficult to explain. When I'm dealing with a standard planned curriculum and trying to impose it on my kids, I'm looking for a way to mold the kids to fit the curriculum OR mold the curriculum to fit the kids. Either way it's a bit awkward, and secondhand, somehow. But when I let go of that and start with the kids, it is more direct. I am working to find my way to what they need. It is more like what I am already doing as a mother.
To put it another way. When I read, say, Charlotte Mason's books and see what I "SHOULD" be doing, it makes it seem dry and like a matter of obligation. Then I procrastinate, and feel obligated to put it on my list of To Do's, and feel guilty when we don't get to it. Then I present it to my kids as a matter of duty, which inspires the same negative reaction in them.
When I read CM's books just looking for things we could be doing, that are worth doing, it's completely different. The intrinsic human value of the activities reasserts itself.
Another way to say it might be that my children tend to pick up on our REAL interests and passions and sense of duty. In other words, "do what I do, not just what I say." I think the great virtue of structured education in the home is that the kids see that education is important to the parents because the parents are demonstrating time and effort and commitment. But you can model that time and commitment and energy as an unschooler, as well.
About "laziness" -- there are two kinds. One is not doing what you should do, and the other is doing it unwillingly, because you feel compelled to. John Holt talked about the person who says "My kids should be forced to do schoolwork, because if I weren't forced to do what I should do, I wouldn't do it." He remarked that this is the mentality of a slave. He is absolutely correct in this; and furthermore, he is squarely in the mainstream of traditional classic and Catholic thought when he says this. Charlotte Mason talks about the importance of Will, of "cheerfully doing the very thing one would rather not do." We ought not to do things because we are forced to, but because we choose to because they are right.