A statistically higher salary works well for luring employees, but doesn't help much retaining them.

As soon as that developer is used to his half a million take home, which takes roughly three years, he'll start looking for a new pasture.

So the understanding has formed that in order to retain employees, you must show them that the grass over there is not actually that much greener. That we also have interesting projects (read: internal mobility), career opportunities and the aforementioned bean bag chairs.