It is an unreasonable maintenance estimate for someone who isn't engaged in a lot of physical activity as far as I can tell.

The problem is not the estimate per se, it is that people don't understand what terms like sedentary and active implies, and tend to overestimate how active they are.

E.g. the vast majority of people who work office jobs are sedentary, whether or not they think that their out-of-office activities makes them "active". An hour of activity here and there in the evening does not get anywhere near compensating for 8 hours in a chair.