And, for me, the main reason is player wages, which are really outrageous in many cases. What happens next? Player transfer fees go down, and you get a crazy system where no one wants to buy the best players in the game.
On the other hand, if the wages go down, then people will just train those players even further (thanks to the NT) and the wages would keep going up anyhow.
This will be one of the few times I will ever say that Hattrick did something better than BB did, but their solution of adding additional skill drops for high-skilled players and slowing training down more based on the skill level (boosting lower skills / slowing down high level skills a lot) was the correct solution to the problem. As bad as the wage-based solutions are intended to be (and remember when guys were over 400k salaries?), people still keep on churning out super high salary players because of the NT/U21 game. If you don't want the game being littered with ten times more 18/18/18/8 big men than there are people who could reasonably justify paying those salaries, make it harder to train those guys rather than just giving people an incentive to create even more.