That's like asking "why would you buy clothes if you think doing laundry is the worst job in the world?" Having kids is great, but taking care of babies and small children is often tiring, boring, dirty, and thankless. Some people like it and that's great for them. But we've also got this massive cultural hangover where we tell women how great and wonderful the job is because for the longest time, we didn't give them the choice not to do it.