Work isn't what it used to be. Seriously. It's not even a secret. Back when your father was a young man, he was expected to find a job - and then keep it forever. It was the same for his father. That's not the way it is in your world. Moreover, most millennials stay with a company for less than 5 years.
We move around a lot more, what's the big deal? It's simple. Any business that has more than 1 employee cannot function without management tiers. Okay, there are a few "leaderless" organizations, but they're few and far between. But, back to the problem. Companies need managers and gone are the days when, "it's Bob's turn, he's been at the company longest."
HR departments, we don't mind telling you, are in a tizzy about this. Who do they promote? Will they stick around? Can they actually lead and manage people? These days, promotion has less to do with tenure and everything with your ability to lead a team. But, your company needs you to demonstrate these qualities before they promote you. How do you do that without management experience? You get in on the MOOC trend. (MOOC = Massive Open Online Courses) Pretty soon, you'll actually be passed over if you don't have a few of these under your belt, so you may as well get started now. #justsaying