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.