and for is the boxscore enough to know "why" you won or lost...as the architect of the game engine I'd say that there are different levels of understanding... on some level "why" is cause you didn't score as many points as the other team.
On a second level you can break down why you didn't score points into two elements. One, how many looks did i get? Two, how much did i score per look? Basically all the info to answer those basic questions are in the box score.
Finally, there is a question of whether the answers to both those questions were really uniform over time.. and obviously they aren't and you need to see the information broken down in time to tease that apart. Particularly if you are trying to see how large an impact individual players.. say player X's poorer defense, affected those variables you want to know how you did when he was in the game.. and particularly how well the guy did against him vs against the other people who were guarding him. Its this kind of detailed analysis that I imagine some smart user who is given access to a play by play type data structure to be able to do....but all users can sort of do it just by seeing where in the game there were big swings and what was going on there.