For newer class-based games like Overwatch, the classes behave so differently and exuberantly that people are going to want to know what ever new flashy effect means. In football, the "classes" blend together and share a common goal. The difference between the Offensive Guard and Offensive Tackle are minuscule to the layperson. However the difference between Reinhardt and Winston are huge, both in terms of playstyle and presentation. Compound this with games adding new classes sometimes as frequently as every three months. That's hard to keep up for the casual viewer.

However you are correct that the objectives in games are usually simple. Push this thing from here to there. Don't let enemy stand here alone. Shoot enemy until no enemy.