Well, the higher power draw cards tend to be more expensive, so in practice budget-focused gamers are already buying lower power parts.

AMD and NVidia have at times competed on power usage, but generally that doesn't sell units to the degree that game support or new features do.

For mobile you start getting traction there because '<vendor>-based laptops have an hour of extra battery life' is meaningful, but gamer laptops are typically designed to be plugged in. The higher power draw typically means more heat and louder fans as well but for some reason noise doesn't seem to be a consideration for most gamers - every gaming laptop I've ever used was unbearably loud.