A few decades ago turnover was much lower and it made more sense for a company to invest in a particular employee. We can debate about whose fault it is that turnover is much higher now and talk about what an individual company can try to do to reduce turnover (be a lot less reluctant to give out big raises for starters) but at the end of the day no individual company can completely negate a nationwide trend.

It simply isn't rational for a company to spend long periods of time on training if it expects that employee to leave not long after he is finally becoming productive.