Weight loss plateaus occur due to reduced body mass requiring less energy, decreased spontaneous activity (NEAT), and voluntary exercise.

“do you just lose linearly one pound per week until you no longer exist and you die because there's no more body weight no we all know that eventually like that plateaus right now part of that is just because you have less body mass so your body has to expend less energy in order to just you know maintain upright posture and those sorts of things but then there's also the neat component as you lose weight you become spontaneously less active”