I think there a lot of people who need to get over it!
I will preface this comment with - this is not a defence of the incident, only pointing out some facts.
There is also a significant difference in the incidents they are comparing. The incident at the RWC had two key elements that helped the citing; physical evidence, and player evidence. The incident was brought to the attention of World Rugby by the NZ team doctors medical report.
One element that was considered unreliable was the TV images. Also the referees did not see the incident.
So the stark difference is if you wanted to cite Franks, it would have been done minus the two key, and overriding factors that helped with the RWC incident, and rely on the elements that were deemed unreliable in the RWC incident.
So, getting to the point, Franks would have been cited on grounds that World Rugby had deemed as unreliable.
Report:
http://www.rugbyworldcup.com/news/97598?lang=en