You see, your company is probably not SpaceX, nor NASA. It's not pushing the frontiers of what's possible, or helping make the world a better place. That iPhone-app-cranking shop is just a marketing gig, nothing important on the face of this planet. And many people, many employees, have dreams. Or seek fulfillment, which they may not find in shipping out yet another webapp. They are in your company because it's fun to work on the problems it has - and it pays well - but that's not the extent of their dreams. Especially in this industry, where a lot of people were originally hobbyist programmers, which means tech is for them a part of life, a part of themselves, and not an otherwise uninteresting money-making skill set.
Happy people may very well leave their jobs, even if they love them, because it's unlikely that their life goals are perfectly aligned with company goals.