I've always explained that I changed jobs because that was the only way to get a promotion / salary raise. Most companies do a default 1-5% yearly increase, whereas when I move to another company, I can get an instant 15-25%.
Things like this are a two way street, yet companies often don't treat it as such.
EDIT: Because you've changed your answer after I typed my response. Some people might be okay with having to stay 10+ years in a company to finally get that role they wanted. I'm not, if I think I deserve better, I'll ask my company for it, if they tell me that maybe in 5 years I can get a better thing, then I rather switch jobs now instead of holding myself back.
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)
It seems odd that there is an assumption that an employee can't provide value within a year.