>>535125379
Because it attacks every single dopamine receptor in your body at the same time. You are rolling for cute girls that love you, you're gambling and winning since it's basically designed so you always win eventually, you're part of a community that accepts you and love the same thing you enjoy, and you feel like you're progressing/achieving something in life.
Gacha developers have discovered a loophole in human psychology to prey on them on a massive level. It imitates everything people are missing in their modern day dystopian world: Love, success, and community.