This might actually be desirable for amazon as it likely helps them keep their employees through the rough holiday season where they probably see a larger than average quit rate. I'd be willing to bet that the choice to quit and receive compensation comes shortly after the holiday season ends, thus dangling a carrot in front of the employees to muscle through.

Really good point -- makes a lot of sense

For a company like Amazon a few months probably isn't significant in the grand scheme of things. They don't operate like a startup that is constantly a few months away from failure. Plus they have a lot more employees to fill in the gaps.