How Come You Can Only Bind Fairies When Cultivating Monsters?

"Apprentice, do you have any grudge against the fairy from Tianyun Peak?" "This one... Respects each other as guests and has never made any enmity." The master frowned, "Then why did you throw rocks at their heads?" "What the disciple hit was not a rock." Bai Chuan was a little embarrassed. "What is that?" "Poke ball." The master sighed, with a sad look on his face. His apprentice had really worked his brain out. What is the name of an ordinary stone called a Poke Ball? ... I have traveled through time, and I have a pet development system. I must find a monster with full physical value, high racial value, good resistance and fighting ability, full learning ability, and a top-notch personality to protect me from the wind and rain! However, why can my elf ball only conquer fairies?