I just realized something
At the beginning of the lightning theif, we hear those famous first words:
“Look, I didn’t want to be a half-blood.
If you’re reading this because you think you might be one, my advice is: close this book right now. Believe whatever lie your mom or dad told you about your birth, and try to lead a normal life.”
So, I’m not entirely sure about when Percy had supposedly written this, but I imagine that these books were after everything had happened-after he had battled 2 wars, lost many friends, and literally went through hell and back.
After going through all of that, especially tartarus, he probably just wants a normal life. He just wants to be a normal kid. He’s drained to the point where a god knocks on his door and all he says is “why?”
Percy Jackson is a kind and caring character, and his fatal flaw is personal loyalty. He gives this introduction hoping to give some demigod out there a better life, he doesn’t want anyone to go through what he’s been through.