There are a few reasons, but the most direct one is that Barbara Gordon as Oracle is able to do things that Barbara Gordon as Batgirl could never do. Batgirl is definitely a fun superhero, but she’s also white, cis-gendered, heterosexual, and completely abled. There is nothing particularly unique about her character. Oracle, on the other hand, is one of the few disabled characters in comic books. Her prominent place in the DCU is a reminder to disabled and abled people alike that the only thing separating disabled minority from the abled majority is their disability (and the prejudice they have to deal with. But that’s not the point here).
It’s different from bringing someone back from the dead, because dead people are not a minority that deserves respect. (They are, in fact, a majority.) To the best of my knowledge, there are few dead people who view Deadman as the inspiration that many disabled people view Oracle as, also.
Also Babs, unlike, many other disabled characters does not exist merely to provide inspiration to other characters in the story. She is a three-dimensional character is who is allowed to be badass, disabled, and relatable. There are not many characters in fiction, period, who fill the roles that Oracle does and Batgirl is certainly not one of them. (Though, don’t get me wrong, I do like Babs as Batgirl. I just feel that she belongs in the past.)
I also really enjoy that Babs is a superhero who doesn’t fulfill the traditional superhero role. Vigilantes on the street are very helpful (particularly if you’re being attacked in an alley at midnight), but it’s also nice to have someone who is able to see the bigger picture and investigate patterns. There was definitely a time period where everyone called her for help and information. Without her, there is no one to provide that information. She provides a greater advantage to the superhero community at large as Oracle. For Barbara to change from being the extremely powerful and influential Oracle to just another vigilante being supported by Batman feels like a major regression.
