Bringing in outside management away from the original company founders is a common way this happens. Especially if they come from another traditional public company that only cares about share prices as the key metric.

I can’t imagine someone messing up Stackoverflow, but Digg managed to do it so there’s always a way (although SO doesn’t have a high quality direct competitor like Reddit...yet.). The best time to take on a business is when they’ve peaked and get distracted, they forget about being the best in the market. I should note I don’t think SO is near that point yet.