The answer, madden is neither a new ip nore is it trying to increase its user base. It has a user base, and it is not the hard core gamer who tricks out their PC. Maddens demographic are people who generally don't game in other genres.
This results in madden's yearly refresh being technically weak compared to true sequels, refining current game modes, maybe introducing a new one, and rarely introducing and new visual tech. The latter is for good reason, madden and EAs other sports games are still being released on last gen consoles. They are strictly targeting the sports gamer demographic which has a console, new or old, and will often be playing offline multi player.
Unfortunately it works, with the 4 console releases (This year they are pushing an IAP system to boot, even selling a second version of a game for 8 total releases that has an IAP bonus built in) and little R&D for updates, it is a cash cow.
Soccer on the other hand, PCs get a higher priority over consoles in poorer countries, especially with the prevalence of internet cafes being used for gaming, so there is still a large overseas demographic for that.
EA's NBA, I haven't looked up the newest one yet but last I recall the engine was usually a year behind and/or the game was based off the ps3/360 version.