Imagine you're an adult in the Pokemon world. You have a family, you have bills to pay, and you have a love for Pokemon. So you battle, even though it might not be the most "responsible" thing to do.
You can swing it, right?
Not when there's a bunch of young punks going around who keep beating your Pokemon. You know what that means, right? Bye-bye, money. The rules are the rules. Which begs the question: as a player, can you imagine how many adult NPC lives you destroy in your quest to become the very best?
Dorkly hilariously illustrates the possible tragedy in this comic:
The fate of all NPC Pokemon trainers [Dorkly]