Why are the smart people NOT in charge?

Because being in charge is kind of boring! A large majority of people in charge are just insecure about themselves and need to exert power over others to feel important. The people who truly are smart don't care about that kind of stuff, they usually have less of an ego.

In addition, a lot of "in charge" positions simply don't require much thought, or not as much as you think - you simply tell people what to do, and these decisions are based on calculated information anyway. Smart people like to do things that allow them autonomy and allow them space to think deeply, or express their skill and creativity. Who do you think is smarter - the CEO of a tech firm, or an electrical engineer? Motocross event organizers, or the riders themselves? A drill sergeant, or a Navy SEAL? CEO of a pharmaceutical drug company, or the doctor who prescribes the drugs?

You see what I mean? The people with real smarts actually get pleasure out of doing the dirty work, so to speak. It's fun for them! They want to get in on the action. But, just telling people what to do from the sidelines is boring. It's a shame how this works out but I think it's true.

This is by no means ABSOLUTELY the case ALL of the time - there are exceptions - just most of the time. It's easier to express it as this model + exceptions.