Sooo, I was running through Aaron Diaz's list of top 10 worst hero/villain redesigns ever and came to a couple realizations; particularly wrt Zatanna and Harley Quin...
In manga, when they want to do fan service in mass market books they come up with a story reason to do so. "Lets send them to the beach and do a swimsuit special". "Oooo, bath house vacation time!" "Just tossed the heroine in the air, lets let her butt hang out of the skirt!!". But, at least the costumes tend to make sense in the broad sense as something people would actually wear most of the time in the vast majority of cases. (I won't deny the outliers exist, but look at 90% of what's in Jump and....).
When NA comics want to do fan service in mass market books, they throw their female characters in stripper outfits 24/7 that no one would actually ever wear out in public to anything but a fetish leather night. One that likely involves an orgy room because those pants on Zatanna aren't hiding either of her holes for more than one or two steps on their own anyways.
Then they wonder why their audience is increasingly 30+ year olds clinging on to their childhood.
Suggestion: It's because no one can get parents to buy their 8 year olds the books once they see that Harley Quin pinup cover.