Keep in mind, this is common behavior through all eras.
To answer the questions mainly right now it's LeBron fans I think and hardcore Jordan fans who became LeBron fans because they don't like Kobe.
Durant was getting some shade during his run if I remember correctly.
However, Curry straight up destroyed LeBron and his legacy. Cats are furious. Dude hit the landscape like nothing we've seen so hardcore fans of other players pretty much have lost their shyt.
Then you have Chicago fans who feel very threatened right now. If Golden State beats their record and takes the title, then they'll have the greatest season in NBA history, non-debatable.
Not saying the above is true for everyone, but I'm willing to bet it's a significant amount and it's my best guess plus observations.
A lot of people really don't want to just accept things and move on. It happens in all walks of life.