They don’t compete or do hard workouts without consuming carbohydrates though. The anaerobic metabolism doesn’t run on fat no matter how much you train, and it brings a lot of extra energy. You simply can’t go as hard as you can without carbohydrate.
Ruminants might be able to convert more fat to glucose, I don’t know about that, but humans can’t. Would be wonderful if we could, considering we can store almost infinite fat but only a meager amount of carbohydrate.
Wikipedia explains it well: https://en.m.wikipedia.org/wiki/Gluconeogenesis
I forgot to mention odd-chain fatty acids besides glycerol, but they also just give you half of a glucose molecule.
This is just more keto pseudoscience. Unfortunately people care more about YouTube videos than what reputable sources say: https://www.niddk.nih.gov/health-information/diabetes/overview/symptoms-causes#type
Not disputing that excess fructose can cause liver damage, but most studies demonstrating this have mice ingesting absurd amounts. This doesn’t happen when you are eating a normal amount of food anyway. Excess water can kill you, but no one avoids drinking water because of this.