Because over the years, there have been various answers from all manners of games in the series. Wario Land 1 had a map screen similar to that in Super Mario Land 2 or Super Mario World, complete with secret exits in levels and an optional world to find. Wario Land 3 made the map a sort of Metroidvania deal with each treasure unlocking new levels or changing the map setup. VB Wario Land and Wario Land 2 didn't even have a map, with the former just having connected levels and the latter having a story progression system (which is itself invisible in the first playthrough). Whereas 4 had a very simple pyramid map and Shake It an equally simple (yet beautiful to look at) globe type map in their games. And hey, let's not forget World with its hub system, or Master of Disguise with... whatever it did. So what solution do you prefer here? Do you want future games to have a world map, a level select, a hub or something completely different?