Two different drivers inside one building
The floor does not care how many people work on it. A large slab needs machine attention on a cycle set by traffic and dust rather than by headcount. The amenities behave in the opposite way: a washroom serving twelve people needs a fraction of the attention one serving a hundred does, regardless of how big the building around it happens to be and no headcount figure will tell a provider anything useful about it.
Quotes that miss this arrive at odd figures. Priced by area, the amenities allowance is generous and the site pays for attention it does not need. Priced by headcount, the floor programme is thin and the building deteriorates slowly in a way nobody connects to the quote. Splitting the two makes both halves visible and correctable and it makes future changes considerably easier to price.
