wow some really harsh comments.
First, not all are like this. You hit their ego and most human being regardless of vocation and regardless of fake or real can't handle criticism. The ego plays a huge part in this. I'm always blown away 2 ways, one that people on here forget that these are humans with human emotions, and 2 that readers go this far.
Readers aren't some magical beings that are immune to criticism. I know the ones i've used I have asked in the past why something didn't happen as they said and I've never had this reaction. They were also very nice and empathetic. The other thing to consider is that some people think they are nice themselves and are snarky or come off as snarky and the person is reacting to this. Also, why do you care if they block you if you left a negative review? I mean if you didn't like them, i'd assume you wouldn't contact them again? Or maybe they said something someone didn't want to hear?
But this goes back to human nature, not all are spiritually evolved. I don't know how many times I have debunked an "educated" person in real life or social media with evidence and proof to back up my claims, they become nasty and name call and get defensive. Why? because you hit their ego and pride and shook the foundation of their belief. Most humans aren't capable of being criticized or have pointed out that they are wrong. Think about your own reaction, there is a very small few that take in stride and will be receptive.
I'm not sure why you'd think these readers would be exempt, it sucks and it's unprofessional, but i've experienced this with all levels of professionals, no one is exempt.