That's a good question. I don't know any tubblrs in real life, but if you take a look at these extreme cases on those shows, like the 600lb fats, the parents clearly have mental problems too. They are usually fat themselves and when they're not, they are enabling it.  In other words, I think the parents of these complete green-haired, polyamorous fuckups would not even think to ask the question "where did we go wrong?" It's probably normal to them.