I care about the mission. In fact, I care about the mission so much that I know that it'll do the company a disservice to train me and lose me a year later to another company with a similar mission offering me more money. Therefore, it's in the company's interest to pay me a competitive salary!
Dwight Schrute said it best: “Would I ever leave this company? Look, I’m all about loyalty. In fact, I feel like part of what I’m being paid for here is my loyalty. But if there were somewhere else that valued loyalty more highly… I’m going wherever they value loyalty the most.”
The best startup CEOs I know overpay their key people BC they know that losing their best people hurts so much more than the same people helping whatever company they might join next
So it sounds like they're paying over market, but not overpaying—they recognize the cost of these people leaving and provide a salary that takes said cost into account.