When you put it like that, it doesn't make sense for the company at all. All they have to do is treat their employees well and fair. Like I said, if my company gives me the opportunity for a promotion and a fair salary increase, then I wouldn't need to jump ship.
I also prefer to stick to one company for a couple of years and make my way up there. But if after a year all you can offer is 1% salary increase, and often no promotion, then as an employee, I don't feel valued at all. (Obviously, this all depends on my performance as well)