When I've asked this question in the past, the most common reason I've heard is that there's a fear, because of the prevalence of other companies poaching engin

When I've asked this question in the past, the most common reason I've heard is that there's a fear, because of the prevalence of other companies poaching engineers, that money and time spent on training will benefit the company that manages to hire away the trainee (and sometimes a direct competitor).