Because majority of people are not suffering and enjoy living so it’s a safe assumption that your offspring will too.

Reproduction also is rewarding in many ways - from biological fulfillment to emotional and philosophical benefits and achievements.

Finally if you’re an atheist that is the only way to leave biological footprint on this planet. Some might even argue its a form of self cloning which I would somewhat agree with as you propogate biologically as well as philosophically by teaching your kids your values.