A college degree is a filter that someone is reasonably diligent, socialized to some level, and compliant enough to play the game. Most employers don’t want some self-taught “I learned the same stuff for $1.50 in late charges at the library” type. If only 1/3 of people attend college, and 1/3 have a high GPA, employers get a filter for the top 11% of compliance & diligence without much effort.