To me the FCA's came off like normal human beings who actually like their job a bit more than average (these people do exist). The people replying to them come off as infantile.
This explains why different accounts swap out -- the manual was designed for a single conversational thread, but employees are supposed to reply to individual tweets (as picked up from some kind of filtering system).
This is a sort of common pattern -- basically whenever I mention a brand on twitter, I get replies from somebody with "<brand> ambassador" in their display name, & those accounts never follow anybody or reply to their replies. It's gotta be a whole industry. The only difference is that, unlike the accounts run by Comcast or TD Bank or Steak-Umms, amazon's manual seems to demand that the service workers pretend to be regular warehouse workers (rather than customer service / PR).
A single person or a small group of people manages a large number of social media accounts in order to pretend to represent a certain group of people. Because so many accounts are managed by so few people (whose full-time job it is to engage with others online to try and change their mind), these accounts tend to not have distinguishable voices or viewpoints, when you're talking to one it's like talking to a robot, or, like the linked tweet says, to the borg.
Oh come on, this is contrarianism for the sake of contrarianism. The overwhelming consensus is that their behavior is bizarre.