Many companies unintentionally incentivize that behavior because the more angry you sound the more likely you are to get bumped to a higher tier support agent.
It's the culture of "the customer is always right" and "the squealy wheel gets the grease".
When acting entitled gets things done, and when management rewards that behavior from customers instead of shutting it down, it's not surprising that more people start doing it.
I think this is a pretty pervasive attitude in our individualistic, quasi-meritocratic American society: we expect things to work right, we get frustrated when they don't, and we get doubly frustrated when the support line doesn't seem to be working either. Then, often, we seek compensation instead of being grateful.
