After my last post, I thought maybe I was being unfair in saying MoS and B v S were the reasons that JL flopped. I thought it could be that people saw it but didn't go see it again or again and again which is what pushes the ticket sales on lots of movies up or maybe it was bad word of mouth. But then I checked and saw that even it's opening weekend was very bad which means it wasn't people seeing it and deciding not to see it more than once and it wasn't word of mouth. People weren't going to see it to begin with which means, as you said, they had already made up their minds they were done with spending money on this particular series. It was a sight unseen decision for most people based on what the series had previously given them.
I think it's unfortunate because I genuinely think MoS was a lot better than it gets credit for being and I really did love the idea of Superman in a world where people react realistically, where bigotry and fearful reactions are a very real thing and so on.