We have no idea what happened at Yahoo. They may have failed two years earlier without Mayer, for all we know.
Yahoo Mail has been a huge driver of their user retention, webmail usage has almost fully shifted to mobile. Facebook has gobbled up a big chunk of display ad revenue along with Youtube and video ads in general. Pretty much everything they can't control sucks for Yahoo.
She had one job. And that was in the company she was with from the beginning.
So she had zero experience working anyplace that is not Google, and zero experience as a CEO.
So she is not qualified and it shows.
Example 2: Robert Nardelli. He was such a great leader at GE. Then went to Home Depot as a superstar and managed to fuck everything up. He also never had a job outside GE, the place where he became superstar.
Anyways why anyone thinks that hiring a CEO that had a total of one jobs, is a good idea, I just can't figure out.