1. Most people who want to manage won't, period. That's just the math, ICs outnumber managers severalfold.
2. Many people will never become managers because they don't seem "managery." They don't dress right, they don't use the right buzzwords, they have a speech impediment, they speak too truthfully. There are all sorts of cultural factors too that people don't admit. For example, no manager would ever say this point 2 to you, because it's too honest and potentially upsetting.
3. A lot of people will only promote you to manager if they think you'll be able to make them look good, and that's the end of it.