I always wondered the same thing, but just never really liked the look of those gauges on the 78/79 tank. IMO Honda made a mistake going away from the 75-77 tank design...
I like the 78/79 setup. The one little fuel gauge always looked out of place to me. Don't know that I want to put a set on the same location but may use the gauges on the 83 project. Starting to come together in my head but that changes often. Might start a build thread soon.