I would imagine they bottled it with the tone of the movie that they had produced.

Nicholsons Joker was an abusive asshole who facially scarred Jerry Halls character just to make "art."

I'm not sure that modern audiences 30 years later would be comfortable with seeing Harley Quinn being backhanded and abused by the Joker.

As his success grew onscreen, they turned Hannibal Lector from the remorseless psychopath who disfigured innocent people to some sort of anti-hero who only killed those who "deserved it."

I can imagine Warner Brothers has the same dilemma with the tone of the Joker. He is immensely popular and his presence in a Batman film puts bums on seats but if they make him too evil and it stops being fun and people stop liking him.

It is a comic book summer blockbuster. After the criticisms of BVS being too dark and gloomy, maybe the WB thought that they should dial him back a bit and make the film more fun and more like what the trailers made it look like it was.