people who have played previous 2k basketball games are not the only ones who are going to buy the game; there will also be many first time buyers. the specific improvements mean nothing to them since they never played its predecessors. The ad has to appeal to as many people as possible. Plus for games that are released annually, it is already implied that their are improvements.
ads aren't that long, and you can't just fill them with word and details; the attention span of the masses is generally not that long. in order to leave an impression on the psyche, consciously and unconsciously, in a short amount of time, its gotta appeal to the senses. its gotta have audio and visual flair, and has to play to peoples desires (theres a reason MJ was talking about knowing and giving people what they "want"). If people are intrigued about the game, they can then do further research themselves, and thats why we have insights and stuff.