No, that part I get, but I mean with Batgirl they decided they needed Batgirl to be Babs exclusively (as far as I can tell), whereas with the Robins and Lanterns they didn't care.^ More likely, in addition to Babs being the most known Batgirl due to the Adam West show ingrained into pop culture, that TPTB love themselves some Silver Age and wanted Babs back as Batgirl.
I think, with Batman, a lot had to do with the fact that Morrison's overarching story wasn't completed. Given that Morrison is a heavy in the industry and his Bat-Story has proven popular, DC really couldn't do a Bat-Restart. Had Morrison's story been concluded, I suspect there would have been a complete retooling of Batman.
That said, Batgirl never really played into that storyline. As such, they could reset her to however they wanted w/o impacting anything Morrison wrote in any major way.
As for the Lanterns, Geoff Johns and Co. got to do what they wanted 5 years ago. There was no reason to change it now since they have that series where they want it.