I think like in any other game, it's just the feeling of getting a reward that makes people addicted to games. In real life, there aren't that many opportunities to be rewarded. In games, it's basically the thing you are playing for. Everyone wants to stand last in poppy playtime and I must say it's very rewarding when you're the one last standing. Though what most people don't know is that the majority of the people they play with are just bots.