Earlier quoted context omitted.
Amazon is firing them for commenting publicly on its business. If you were employed by a company and disparaged them publicly, breaking company policy, would you believe that your employment with them is in any way protected?
I agree with you. Amazon, should though, be aware of the Streisand effect. They are amplifying their problem by firing people instead of, say...reprimanding them.
It doesn't sound like Amazon is attempting to hide anything here.