There is one additional perk to exercise as opposed to tasks. Work tends to involve straining physical repetitive labor. Dedicated exercise can be more targeted and fits differing constraints. Of course vanity is part of the reason for that optimization - just like a full body tan is more 'fashionable' than a farmer's tan working out can focus more on 'mirror muscles' than practicality.

Just look at Olympic weightlifters - they tend to look plump but they certainly are well strong as Olympic weightlifters.