Why isn't a scale the best judge of body fat versus lean mass?

A scale measures total body weight but does not differentiate between fat, muscle, bone, and water. Lean mass can be significantly denser than fat, meaning someone with more muscle may weigh more yet have a lower body fat percentage. Additionally, factors like hydration levels can cause weight fluctuations that don't accurately reflect changes in body composition. Therefore, methods like body composition analysis or measuring skinfold thickness provide a more nuanced understanding of body fat versus lean mass.