Actually going through a lawsuit is expensive, “bluffing” long enough to send a nasty and credible letter can be relatively inexpensive.
Importantly it’s also getting moderately expensive for the other side which really discourages this kind of behavior. Suiting an arbitrary person you have no connection with invites a counter suit for wasting their money, but that largely goes away with such a one sided provocation.
Through discovery you can get the name of the parties involved from Amazon, but Amazon is very likely to drop them as a client solving the issue.