There are Way Too Many Young Children.
Even if they don’t seem like much when you’re 30.000 feet in the air, seatbelts can make a significant contribution to the reduction of turbulence. If you are seated more securely, you will have a lower risk of becoming sick due to motion sickness when the airflow changes. Attempting to make a big deal out of it is pointless and unnecessary.
In the end, doing so is for the best of your interests! When a flight attendant reminds you to do so in the future, make sure that you continue to fasten your seatbelt at all times. If you hit your head against a bulkhead, you are going to be in a lot of pain for the next seven hours.