Now that's an interesting experience. The only answer I've ever got from that exercise is "that's what it says in the zoning ordinance" or "that's the law." Not that those are wrong answers, but they're not very informative.
My favorite was trying to get an explanation for why, since the zoning ordinance prohibited a guest house from being more than 600 square feet and from having a basement, I was required to put in a septic system sized for a 3 bedroom, 6 occupant, dwelling. The answer was right - the house size restrictions were in the local ordinance, and the septic system requirement was in state law (with an unexercised option for local modification).