thejakeformerlyknownasprince Answer:
One word: consequences.
Many words: In Percy Jackson, killing a monster momentarily inconveniences that monster - it’ll be back in a few months. In Animorphs, killing a monster means killing a person with friends and family who will now miss that person who is gone forever - oh, and every time you kill a monster, you also kill an innocent prisoner of war.
Percy Jackson has a major plot hinging on Luke betraying his friends for reasons that are sympathetic as well as selfish, and though Luke chooses to die to save his species, it’s also implied that Luke has earned Elysium. Animorphs has a major plot hinging on David betraying his friends for reasons that are sympathetic as well as selfish, and this leaves his friends with no choice but to trap him in eternal body horror until such time as Rachel is implied to have killed him. It’s canon that on death, Animorphs - including Rachel - “dissolve into nothing.” Percy has to choose between letting Annabeth die and letting Kronos take Earth, but finds a third way out where no one dies. Marco has to choose between letting his mom die and letting Visser One take Earth - and then murders his mom. The Animorphs are tortured by the assumption they won’t live to adulthood; Percy is tortured by the question of how to use immortality responsibly. So on.
ani-tolaat-bli-toelet:
I think it’s at least partially because Percy Jackson is a legend while Animorphs is a warning.
Percy Jackson started as a way to empower a little kid with ADHD, it grew into a story about using power responsibly and what it means to have friends you’d die - and live - for.
Animorphs is about the consequences of war, how taxing it is on your soul and how you can’t win pleasantly - you either play nice and die or you get your hands dirty and survive.