Map content is very sensitive, and is nothing like a programmatic entity's source. There is no need (or automatic capability) to structure the source code of a map, not to mention the fact that messing with map's source might mess up your map.
The only thing that might be worth structuring are the processing rules embedded in the map. However, the editor for these rules is somehow limited, and the command STRUCT is not included in it. For processing rules, you can struct your code manually.