Why do people still think it is ok to give candy as reward even with all the childhood obesity?

More complex!: 2 issues: is it necessary to offer any rewards period? Does offering candy cause obesity? Your question is difficult to comment on since obesity prevention's low lying fruit to chip away at is sugar and processed foods. Portion control, activity, decreased screen time, and a diet with more veggies, fruits, and roots is the rule one should really set. Limits and rules will carry families through.

Food & Love: Families are pretty consistent about equating food with love. To reward children, a food treat is often offered. It's a mindset going back too many years to count. Today there are many cheap, unhealthy, but tasty options because of artificial processing of sugars & fats. Working with families to steer away from these rewards but it's built into our culture making it difficult to change.