You're making a nuanced point but it's correct. Good managers can give a little motivation (mostly by talking about and finding the right areas to work on for those people that don't otherwise already know). But for the most part good management is buffering the core that allows individuals own motivation to be self-sustaining (and productive over time) and also making sure that people aren't on a path that won't be useful (i.e. the manager knows the company will never fund phase 2).

Good managers will help you find your own motivation and set you up to follow it. Bad managers will kill it.