Teams that have success in BB, typically train there own star players. Having a good trainer allows players to train significantly faster, which in turn makes the team better.
IMO BB is all about good training. It wins games and makes money. To buy well skilled players is extremely expensive, training them is relatively cheap in the overall picture.
I have a player that is likely worth 3-5 million. He has been trained on my team since day one. The trainer for him cost $490,000 over the three seasons. I consider that a pretty solid investment.