People don't exercise free will because of factors like biological determinism, environmental and childhood conditioning, and the influence of subconscious patterns. The idea that their choices are pre-determined, either by genetics, prior events, or even the functioning of their brains, can diminish their belief in free will itself, leading to less effort to make different choices. Additionally, things like stress, sleep deprivation, and social pressures can further limit conscious control over actions, making it seem like they are slaves to their inclinations.