Regarding Snyder's box office track record, he's mostly directed movies with a higher than normal degree of risk (although almost all movies, even ones that look like no-brainers, carry significant risk).
His first movie, Dawn of the Dead
, had by far the lowest risk factor. It had a low budget and there's a solid, consistent market for horror films, especially brand name horror films. And Dawn of the Dead
was indeed a big success relative to its budget.
His movies after that were a lot riskier: an R-rated green screen historical action movie, a very dark, very violent and very long R-rated superhero epic with no big stars, a CGI animated movie for a studio that, despite its long and storied success in animated television series and film shorts, has struggled to sell animated feature films, and an esoteric action movie with a cast centred on young, mostly lesser-known, actresses.
Directing a Superman movie is a much safer bet for Snyder than any of his other post-Dawn of the Dead
movies. After all, if a Superman movie designed as an introspective drama that split moviegoers and had many complaining about a lack of action could nonetheless make just shy of $400 million worldwide then it stands to reason that a Superman film with Zack Snyder's penchant for massive action scenes has a good chance to make a whole lot more.