It’s a good idea because when you WANT to be at your school you will do better in class. It’s a reason to do well, an impetus towards you achieving your goals. It also gives you a reason to give back to your school, to want to contribute to the overall welfare of your peers and those who will come after you, so that they can have the same pride in their school as you did. Getting into the habit of those contributions serves you well later in life, contributing to your neighborhood, your workplace, etc, which makes life better not just for everyone else, but for YOU.

(You may not want this part in your essay, but it’s part of my answer)…

You keep hearing from lifelong losers that they hated their school, or they thought it was worthless, etc. Most of them barely graduated, or didn’t graduate, or are antisocial or asocial.