After multiple CEOs in the last few years, it would be interesting to hear an impartial insider's analysis on what went wrong. Marissa Mayer came with decent cr

After multiple CEOs in the last few years, it would be interesting to hear an impartial insider's analysis on what went wrong. Marissa Mayer came with decent creds, a sizable runway and support from both the board and employees alike (at least in the early days). Why is she unable to make any progress? Was it just a better support circle @ Google or just unlucky and bad decisions?