Keto or just low carb is certainly of value to a bodybuilder as it allows one to strip off body fat quickly.
The problem long term is that it’s too restrictive and people get tired of the limited options.
Why does it have to be the only way you ever eat again? When you get sick of it, take a break. Any eating regimen that gives you above average results is going to require a level of sacrifice. The reason high fat, high protein, low carb protein diets appeal to so many is because many people think they feel a lot less restrictive than traditional eating plans. You keep saying it's too restrictive, but that isn't really a given.
If the crossover concept is true, then that lends credence to what many say about carbs. They are useful when doing high intensity activity, but don't burn off as easily with moderate intensity. If you aren't running a marathon, maybe it is much smarter to stick to foods that are higher fat, higher protein. I can speak from personal experience that you can get through high intensity weight training workouts on high protein-fat/low carb.