I think the cause may be wanting a way to opt out of the pressure cooker that modern life is.
I'm disabled (I have MS), and the one benefit to it is that I have a 'get out of social expectations free' button I can push if things get too difficult. If I'm not feeling well, it's acceptable for me to cancel plans, call off work, make sub-optimal decisions (putting my health above my earning capacity, etc.).
In short, disabled people are allowed to be fallible, have needs, and make mistakes. I think that the kids feel under too much pressure and want a release valve for it. An invisible disability gives them a 'this is too hard, I need out' button. Disabled people are also given some empathy, and that is at a major premium right now.