It's a completely different world, and some people aren't made for it. Among other things, the politics of management positions is often pretty intense, and not something that engineering-oriented people find fulfilling.
ICs like to think they don't have to deal with politics. It is only an illusion that sometimes is true because their manager happen to protect them from those (double-edged sword: hurts visibility) and if they are lucky their interests are aligned with the boss. ICs often have a worse hand in politics because they have to fly blind in the politics world and operate with less information and visibility.