My biggest concern about focus on weight loss as the metric instead of "healthy lifestyle" is that losing weight is easiest when you do it in an unhealthy way. Crash diets are a good example of unhealthy weight loss.

Another funfact is that you can literally go to bed for a few weeks, let muscle atrophy kick in, and lose more weight than any diet+exercise regime. Won't make you healthier, but you'll lose the weight. Yay metrics!