They decided to make Zach Snyder the standard that all movies should fit into.
The problem is that DC movies were practically dead after the 90's fiasco that was Batman and Robin. Christopher Nolan came along with a good idea to do a darker, grittier, "realistic" take on Batman. This worked well because it countered the stupid cheesy tone of the previous Batman films, and because it was well-written/planned (Nolan's first two were, anyway).
And because the studio execs for Warner Bros. are dumb, all they took from that is "dark and gritty + CGI = money" so they have been making the movies with that formula. They ignore thoughts like good writing, dialogue, pacing, a balanced approach to CGI, etc.
And yes, Zach Snyder just perfectly captures everything wrong with that mentality. He's the wrong fit for what these movies should be.