In the spirit of customizations and options - which I believe this forum has a favorable opinion on given the love shown for the return of player editing features - Tiburon decided early on that the user should be able to spend his players' earned XP however they want.
They do, however, provide strong guidance about the best paths to upgrade a player with how much each attribute costs to upgrade. If a user wants to do that against the guidance provided by the game, they aren't going to actively prevent that. For example, be honest, when's the last time you or anyone you know spent the absurd amount of XP required to upgrade SPD one point? Are you really that offended if someone else you are playing against uses it, knowing how much more they could have upgraded his player if he bought multiple attributes which cost less?
Meanwhile, you still are provided the option to only spend XP on the things you practiced if that's how you choose to play the game. There is nothing stopping you from custom-tailoring how you experience the mechanic in that fashion.
Nothing.
In this case, video game usability and consolidation of mechanics won out over "sim", and game is a better experience for a wider cross-section of Madden's fans because of it.
Requiring a user to play specific drills with specific players to improve specific ratings is tedious and unnecessary micromanagement, and playing drills with 53 players a week would take way too long and put too much busy work between users and actually playing games. In contrast, the more reasonable approach of leaving that all to a predictable menu-driven simulation of weekly tasks (such as Game Prep in M15 / M16) isn't engaging in the slightest to the
average console gamer, either (as in, someone who isn't on OS and doesn't already have a deep understanding of football).
What exists now with training is a happy medium. It doesn't take too much time so it never feels like it's in the way of playing games and advancing further into your league. It actively teaches new users how to play the game by funneling them into Skills Trainer, which teaches high-level football concepts. It requires the user master the components of the game taught in the drills to succeed at the game, since all the XP rewards are based on drill results. For "sim" players, it's also authentic, since the drills run again all use real-world football concepts and are taught in believable contexts. It's fundamentally sound game design.