Point is that you can cap player faster w8 higher lvl trainer.
You can train high profile players for profit w8 smaller pot. And you cap them faster(sell them faster).
If your goal is to have NT player, you will get money from merch in return!
If your goal is to have a NT player, get a trainee who is 18yo with high skills and high potential. If your trainee sucks, you can have the best trainer in the world and your player will grow up and never make NT (unless he's from a country with no users). However, if you have a top-notch trainee and train him seriously with a 4-5 coach he will very likely make the NT. but whatever, people do what they think is best.