This is also the same problem with the entire H1B situation and why Google, Apple et al. have made some pretty poor justifications of the price-fixing collusion: because they've avoided investing in on-going education to such an an extent that the only thing they've been able to imagine for getting talent is poaching it from other companies (leading to the on-going upwards price war).

They could easily solve their problems if they actually wanted to train people, and promoted those who would/could mentor more aggressively.