Basically, Warner Bros. at the time, seemed to have this twisted philosophy that they needed a big star to save a movie. With Batman & Robin, it felt like Warner Bros. believed that George Clooney wasn't a big enough of a name at the time to draw money, hence why they brought Arnold Schwarzenegger in as Mr. Freeze.
Was Schumacher's idea as well to hire Schwarzenegger, Schumacher did like having all star casts or young hot actors in his films.
It's best to hire a character actor to take on the role of a super villain.
WB at that time did seem to be making a lot of junk like Batman & Robin, Steel and Wild Wild West. Not giving a damn about quality or what audiences would like to see.
Fans were probably hoping Mr Freeze would've been like his TAS version with his stoic robotic voice and demeaner, which they didn't do they went the way he is.