In theory the company can instead hire trained employees whose training is paid by the other companies, and not invest anything to train their own workforce. And that ultimately leads to no company investing into training, other than the bare minimum.
In theory after training you can demand a salary higher by at least the value of training.
This. It is much cheaper for me to hire a fresh masters in telecommunications and spend 6 months in training than to hire a 15+ year industry veteran with no college education.