I’m not sure why you are insisting that parents taking on this extra burden while working (from home or not) is an unreasonable explanation for this.
I'm not insisting, the experts are. There's plenty of data that shows that this is necessary if you want a child to have normal development. Unless, of course, parents are paying for high-quality care elsewhere, which has been shown to give similar advantages.
And what's unreasonable with expecting parents... to be parents? I don't understand why any child should be disadvantaged because their parent(s) decided it was too much work to actively care and participate in their development.
When my kids were young, I was working full time, while my wife's career was put on the back-burner so she could take care of them. I still had to come home from work, help her with the kids, often staying up until 3am with a baby who had colic, then get 4 hours of sleep before heading out to work to do it again. My weekends were devoted entirely to the kids, and my wife would have a bit of a break.
It was exhausting. I get it. But it had to be done. My eldest didn't even have access to TV until she was four, so it was all about books, interaction with other kids, outings with us, and library visits for their programs. Then it turned into kindergarten, and we were still putting our energy into her development. And as she got older, it was sports and other activities that required a big commitment on our end... it really doesn't end!
Child-rearing is by far one of the most committed things a person will do in their lifetime. More than work. I don't envy anyone who has to split their time between a demanding job and their child or children.