Why are people fascinated by this trial and so invested in Depp winning?
To me, Depp and Heard just seem like stereotypes: a pair of wealthy Hollywood narcissists in an ugly, toxic relationship. It isn't very interesting.
What has been interesting is observing how fascinated people on social media are with this case, and how one-sided the support is towards Depp. Heard doesn't strike me as a stable or nice person, either, but Depp is a well-documented alcoholic and drug user with anger management problems, and has a crazy amount of money and enablers surrounding him. Yet he gets the lion-share of the public sympathy. Look at some of the comments on the MovieChat forums about Heard - they are incredibly nasty.
I get the feeling that a lot of the ill-will towards Heard is inevitable backlash / fatigue from #METOO. I'm also intrigued by the theory that public sentiment is being deliberately manipulated on social media and people are just following whatever they see in their feed: https://www.rollingstone.com/movies/movie-features/johnny-depp-amber-heard-fan-war-online-social-bots-1345208/