We often hear about how back in "the day," employees were loyal to companies, and the companies were loyal to their employees.
Now, I'm not sure how true that really was, but it's certainly something that we're missing today. Companies want the most out of their employees before tossing them aside, so of course it's fair for employees to expect the same of their employers.
Companies that are more willing to invest in their employees are, on average, going to get more buy in from those employees.
It's really not that complex in theory. Based on how rarely it happens, though, it's clearly much more difficult to execute in the real world.