Back in my youth the Olympics were the realm of amateurs, and a lot of energy was devoted to policing the line between amateurs and professionals. I guess amateurism was the last refuge of the WASP hierarchical society; sports was limited those who had the money and the leisure to train for events and participate in meets. My impression is the horse events, like dressage and jumping, are the remaining holdouts, but maybe I'm missing the sports without sufficient appeal to pull in a paying audience.
Speaking of audiences, in my youth track and field was the fourth big participation sport, with horse racing and boxing the big audience sports. (Early TV had the Friday night fights; yes, a professional fight every Friday night, to go along with the bigger events like the Carmen Basilio-Sugar Ray Robinson fights.) The interest in track and field has dwindled, and the shrinking interest is shown in the meager coverage it gets outside of the Olympics.
Meanwhile the big three of basketball, baseball and football have gained prominence. One benefit to those sports, as opposed to track and field or boxing or horse racing, is statistics. Particularly these days you can lose yourself in the statistical analysis of players and games. Track and field events don't have that complexity; the only thing they have is ever more refined measurement of results.