There are more reasons to exercise than just to "get stronger." Here are a few reasons why:
You sleep better. Sleeping better can improve your mood and it just feels really good.
You feel better. It feels good to be healthy. Your body likes being healthy.
You grow more blood vessels in your brain. Your brain needs oxygen to function. When you exercise, your blood flows better. And your blood brings oxygen to your body and your brain.
You get stronger? Wow who could have thought? Yeah your mussels get stronger when you exercise.
You can socialize with other people who like to do the same thing(if you like that kind of thing)! That's the best part of being on a team sport is the team. They encourage you to have fun.
Those are some reasons you should go outside and have fun.