People gravitate towards the workout intensity of those around them.

So, when exercising next to high fit people working out hard you try to keep up with them while exercising next to lower fit people tends to slow you down.  And not surprisingly, you tend to enjoy your exercise more when you do it outside compared to exercising indoors. 
Full article 🤝 https://www.scu.edu/illuminate/thought-leaders/thomas-plante/why-your-exercise-environment-matters.html