In the first chapter of Joker War, Batman says that The Joker sees people as just meat to be slaughtered. As Joker killed yet another room full of people I realized that it just doesn’t really matter. There’s no shock value if Joker is just going to kill 50 people every time he appears. The reader is desensitized if Joker is killing people left and right every time he shows up.
In his first appearance he called out a few specific targets and Batman had to figure out how he would do it. In the past decade or so it seems like Joker kills countless people before the story really gets started. There’s no real suspense or intrigue.