I've already said that. If someone comes here and says that if I can develop a player, he will be a major help to my team, and that maybe he can go to a NT, I would surely train him. Of course not everyone thinks like me, but there's always the ones who do.
And another way to do it will be with Training Game. Many players don't want to wait 3 seasons to have his player on NT. If they see a chance of having him there, even if it is for only a game, I think they will try that. And even if they don't win, they'll go like "Wow, I've actually managed to get a great player!"
Other thing that many players aren't aware of, is that when training only one position, they'll get to the end of 2 seasons with 2 excelent players. And by selling one of them, they will get a lot of money to reinforce the other positions.
In the end of this past season, I had 2 players of 19 years. One of them was already shown here, the other was some steps behinddue to injuries. I sold the second one, and I got 750k. With that, I could easily get 2 players for my team. And their salaries were only 7 and 10k so that's not a problem