During the DC's prequel storyline to the New 52 universe known as Flashpoint, DC made some radical changes to many characters in the DCU as the Flashpoint altered the timeline. Zatanna was one of those changes.
Here you see Zantanna before and during Fashpoint. In the alternate timeline of the Flashpoint event, Zatanna is a member of the Secret Seven and also is a member of a motorcycle gang, her father Giovanni "John" Zatara was transformed into a motorcycle when Zatanna is riding on him. Zatanna is killed while trying to cast a death spell on Enchantress.
Now I have to say that even with this altered history as a Bike Babe, it is my opinion that her outfit is VERY extreme looking more like a New York city street walker instead of a Hell's Angel. Heck I have been in New York at night and those "street walkers" dress better then this! I mean look at those pants! I understand the concept of low riders however if these were any "lower" they'd be nothing more then a pair of pant legs. Combine it with her Jacket I say that Zatanna was just looking for an way to let everyone know she enjoys wearing leather undergarments.
Oh and Just for reference this is Zatanna's new look after Flash point in the New DC 52 Universe:
Though it most be noted that she still wears she classic costume when on stage in her job as a Stage Magician.