Most water heaters come from the factory set to 140 degrees. Most households never need water anywhere close to that hot.
That's not a small gap. Every degree above what you actually use is energy spent heating water that just sits in the tank, losing heat, waiting to be reheated again, in a cycle that runs all day whether anyone showers or not.
120 degrees is hot enough for nearly every household — hot showers, clean dishes, laundry, all of it. The dial is usually right on the unit itself, sometimes behind a small panel. Takes two minutes to turn down.
The second thing nobody checks: the tank itself. If you can touch the outside of your water heater and it feels warm, that's heat escaping into your utility closet instead of staying in your water. A basic insulating blanket, wrapped around the tank, costs about twenty dollars and cuts that loss significantly.
Between the two — turning the dial down and wrapping the tank — you're not spending anything close to what a new water heater costs, and you're not asking anyone to change their showering habits. The unit just stops working as hard for water nobody wanted that hot in the first place.