The problem is that there is a misalignment of incentives. In this scenario, the execs wanted the hire done, so seeing the long odds on that happening motivated them to do the hire, and it got done and they were happy. But from the point of view of the bettors, they just lost their bet! The next time they make a bet, they will remember this and avoid betting on markets like this (ones where execs can read the market and change course) and so those markets will have fewer informed bettors.

The execs will then end up with lightly-traded, inaccurate markets on events they control, but probably still reasonably accurate predictions on events that they can't. That is maybe still useful, but it means you will have to think hard about the nature of each market before offering contracts on it, which may not really be easier than just doing the forecasting some other way.

It's like how there's an inherent value to adding numbers together on a calculator. It "just works". Once you have it, you can rely on it to do the math part while you do more complicated things.

A prediction market that is a dance between observer and market and agent doesn't "just work". You can't rely on its predictions because they are conditional on your choices, it's a complex feedback loop.

Yes, that's what a "prediction market" is.