let's just put it this way....
in real-life, a young player plays, every game he play, he learns... every time he learns, he 'develops' so to speak.
in BB, your player plays, gets tired, every game he play, he adds up his minutes in training, training is only every thursday/friday (depending on where you live) and that's the only time that your player will learn. he does not learn everything in league games (as far as i know, only experience has gains in league games)
also an additional... in BB, the recommended 48 minutes per week is the best time that you have to have in training. best time meaning that the player is guaranteed he will get full training, and it's up to the player if he will get enough training results for level pop.