According to a recent study 54% of Americans between the ages of 16 and 74 read below the equivalent of a sixth grade education.
Why does this matter for Social Security? That 54% account for the vast majority of disability claims, particularly those disability claims which are most likely to generate appeals. The thing is that if you develop serious health problems, you have something to fall back on if you become disabled if you've got good mental abilities. If you're a fire fighter, for instance, and your knees give out but you're not too old, you may be able to switch to being a 911 operator, for instance, because you have a little background in the field and you probably have enough intellectual ability to learn a new job. However, if you're a roofer, you may not be able to make the transition to being a roofing estimator, for instance, because you may not have the innate intellectual ability. (I'm sure there are plenty of smart roofers but it's hard, dangerous work with poor pay so who do you think ends up in these jobs, for the most part? Did you think people take roofing jobs simply because they like working outside?) Add in increased age, which reduces adaptability, and switching to work with fewer physical demands but requiring more intellectual ability becomes extremely difficult. Don't think that age makes a difference in adaptability? You're almost certainly young. Wait until you're older. You'll understand.
There are those on the right who honestly believe that way too many people are approved for Social Security disability, that those people may have some health problems but that they could easily switch to less demanding jobs if it wasn't so easy to get Social Security disability benefits. Well, it's not at all easy to get Social Security disability benefits nor is it easy for most of the workforce to switch to less physically demanding jobs.