Yeah, but if they just let CPU teams sim practice every week, the whole league will be filled with players with 90+ ratings, several per team, before very long.
The whole progression system needs work. It's a tough balance: users want to be able to improve their teams through effort and be rewarded with competitive advantage. On the other hand, if you allow for too much reward, it breaks the sompetitive sim.
This is not a problem unique to Madden. In NBA 2K14, the Association mode lets you skill up your GM and training facilities to the point where any drafted overall 60 rated rookie could be so boosted that he's playing at an overall of 90+ before his rookie contract is up.