What I have seen was the cost spent on training was considered wasted when the training was finished, employees left to another company who could pay more, since they didn't spend money on training.
Granted that companies do not have the enforcement teeth as the U.S. military, but this is the way the system worked back a generation or two ago.
My Dad stayed in the Naval Reserves for 20 years after World War II ended because that was part of the agreement of sending him through OCS to train for his particular skill set.
He barely missed a Korean call-up because my eldest brother was born in the summer of 1950. By the time a Vietnam call-up loomed, he had six kids. But he still dutifully reported for his two weeks of reserve training every summer until his contract was discharged.