Because I worked there, and I saw first hand the way that company is run. I've worked for a wide variety of companies, including what is now HP and Microsoft, a number of startups and a number of medium sized companies. I'd rank Amazon as the worst company I've worked for, and even Microsoft was a bit better (there's on startup between the two in the rankings for the suckiest environments).

Amazon is a very employee hostile place- all advancement is due to politics. Unless you have a good manager (and there are a few, mostly engineer who have been there a very long time) you can't advance unless you play really vicious politics-- and I mean, sabotaging others work kind of vicious. The people they bring in as managers (because they claim engineers don't want to be managers) are people who have no management skill.

I may have had one of the worst- his only training was in "criminal justice" and he clearly thought he was a prison guard... he'd regularly chew out the whole team for failing to do things that he didn't even understand weren't our responsibility (or in once case something we had actually done, but some other manager had told him we hadn't and of course he knew absolutely nothing about software so he had no way of knowing whether we'd done it or not.)

Maybe microsoft is that bad now- it was heading in this direction when I worked there...but Amazon was the worst place I ever worked. (And I worked for an educational startup where all of management was gradeschool teachers who also didn't understand technology and treated us like grade schoolers... and this company had trouble making payroll... but being belittled is much better than being verbally abused in my book.)