Frank Sinatra was among the anti-rock and roll crowd. It would be sweet revenge to induct him.
Clearly you're not a fan of the Pretenders. However, I think you're ignoring a significant influence that Chrissie Hynde had, namely on all the female rock and roll that came after her. Ask any grrrl rocker of the last 25 years who her influences are and Chrissie will be in the top two, and I'm hard pressed to think of the other.
Influence is often a key selling point for Hall induction