Because parenting makes you a better person! It's true.
Background: My inlaws are forever pressuring me to have kids, and that's one of the reasons they want me to! Seriously, they think it will make me a better person (I really think they think it will knock me down a peg or two and stop being such an independent woman). So every time I see one of these and if I am in a snarky mood, I send it to them with the subject: Because parenting makes you a better person.