Based on some stories from my mother, I think you’ve nailed it. A lot of people seem to be getting on SSDI these days. She just can’t understand it.
Those are numbers of SSDI recipients in *1,000s*. So we have today almost 9 million SSDI recipients, as compared to around 3.5 million in 1993, around 20 years ago. Our population certainly isn't up 2.5 times.
Lots of other info at the link as well.