People are particularly bad at self evaluation.
Keep in mind, most people don't know what their IQ is. And most don't consider themselves to posses less intelligence as they don't know what more intelligence feels like.
See this video for relationship between job expectation and IQ: https://www.youtube.com/watch?v=fjs2gPa5sD0
People with a level of intelligence that is measurably above average can still have difficulty finding and retaining jobs. There is a large group of people who can be expected to take whatever jobs they can find, out of necessity, regardless of their skills and aptitudes.