because no theory truly describes all possible situations. I believe that using loss aversion (I don't know prospect theory sorry) doesn't work great for sports because it worsens performance instead of improving it most of the time (there is a place for it, see below). Think about free throw shooting. Coaches teach their players to think about the process of shooting the free throw (i.e. routine, or sometimes think of nothing) instead of thinking about hitting the shot so they don't lose. Why? Because thinking about avoiding loss increases stress levels, which leads to tightness in muscles and a lower likelihood of getting the basket in, or in other words a poorer performance.

When players are not performing well (in basketball) you may see a coach yell at players to try to raise their level of intensity if they aren't doing great (this sounds like loss aversion a little bit). Most great coaches follow this up by giving a set play or focusing players on proper technique for what is lacking (boxing out, proper screens, etc.). This then relaxes the players and focuses them on execution and not on winning/losing. Many fans focus on the coach's actions to increase awareness (yelling) but don't notice the calm instruction getting them ready for the next play or proper technique.