& @ JohnnyB:
The majority of BB managers are coming from countries such as Spain, Italy, Poland, USA. In these countries there are 20 to 50 times more teams than in yours. As a consequence the density of talent is such that you cannot get your player in the NT without extremely focused use of resources. What is best to create a very skillful single player is not necessarily the best for the ligue team. This concern at least 2 areas:
1) Training (extensive use of one-position training; design of plan according to the needs of a single player)
2) Financial resources (distribution of salary vs total team performance; value creation through training)
Here an extreme example of a focused team. The player has the second highest salary in the Italian National Team which currently leading the BB world ranking
(4211248). He is earning a salary about twice as high than his other 16 team mates in total. I agree, it's extreme and it is chosen to be didactic ;-)
I am not saying that you can not have success with your team while developing players for the NT. I just say it slows your team down and this effect is more and more important as countries are bigger.