Young players are eager to join BvB as the club holds 'stepping stone' niche in a feeding chain. Youngsters know they'll get a chance to develop under good coaches, play in a strong league without any pressure to win trophies, and then will be moved for a hefty price. BvB's outstanding scouting is a myth, they just have more margin for error than top clubs and can deal with a huge turnover of players.
For example, Dembele was known as a future worldbeater when he signed for BvB. All top clubs were after him, it had nothing to do with scouting. Showed his quality and was successfully sold to Barca.
On the other hand, they tried Mor, he failed and was moved on, etc.
Txiki is the most successful squad builder of last 2 decades, he and his team have nothing to learn from Dortmund.