1. Interesting. I was under the belief that disability benefit requiments basically meant "unable obtain and maintain full time employment due to a disability". After some research it seems it's more about how much money you earn than how many hours you work.

2. Are you not conflating Part Time/Hourly and Full time/Salary?

70% of Americans work full time and just under 60% of American workers are paid hourly wage.

For example, every factory I've worked in has been Full Time hours with hourly wage pay.

It's mostly Managerial/corporate positions that are salaried afaik.