While they may make above average in the overall assessment of income for a country, they make well below average for the type of work they are doing. Many game companies know they can pay below market wages because of demand for the jobs.

Source: When I quit game dev, I got a 60% raise and I was on the higher end of the pay scale at that game dev job. I know lead developers with nearly 10 years of experience making under 70k in games. I frequently offer them roles that would double their salary and they turn it down because they like working in games.