That's because they're fucked in the head more than anything. There's medical case reports of morbidly obese individuals going on supervised water-only fasts for OVER A YEAR and having massively IMPROVED bloodwork (yes, being obese is that bad for your health). If a normal weight person tried anything close to that, they'd likely die in a few weeks from starvation. But normal humans can fast for decent periods in spite of the lack of massive energy reserves simply because they have a shred of conscious control over their actions, unlike hambeasts.