Like any other genre of drinks, you have beers that have moved up the list and beers that are way down. Same with soda's, tea's, and other beverages.
Budweiders moves a lot because they have deals with stadium's, concert venues, and huge venues where you only have one or two choices. The rise of the microbrewers have made choices for all of us. As for light beer, well.. less calories makes people think less beer belly.