I have never been an employer , so this post is entirely supposition.
It costs money to train anything to anyone, You can't flip burgers until you have learned the approved flipping method, so some training is absolutely unavoidable no matter what it costs.
While your trainee is in training he is just not earning much money for you, if the minimum wage rises , the margin will close even more.
At some point the trainee will know enough to cook edible food , drive straight nails or stay between the white lines, then he will begin to make some money for you. His pay is a minority of his employment overhead , but it is this entire employment overhead that determines how soon in the training the trainee starts being a productive worker.
If the training period takes too long , perhaps you can't afford many trainees at one time?