You're saying "good developer". What if not all your developers are good? Remember, someone is employing the bottom half of the bell curve, and making money with them.
In a lot of cases, they're making money despite them, not because of them.
I suspect in most mid and large sized companies that the top 10% of developers are creating more value than the next 50%, and that below that, the value could easily be negative.
I suspect in most mid and large sized companies that the top 10% of developers are creating more value than the next 50%, and that below that, the value could easily be negative.