Tldr politics, glass ceilings, re-orgs, purposeless/abandoned projects. As a former Googler, I can see why people post these: internally Google is hyper-evangelized as the best place to work ever (why would you work anywhere else). When leaving, its a necessary step to form a good argument for yourself as to why you've decided to go against the culture. The personal spin makes it an interesting read.
I always find the "best places to work" type lists a lot of crap. Usually its just a case of biggest and best known companies. I have worked for a real mix of places and the biggest companies haven't been any better than the smaller ones. Usually a good manager makes a far bigger difference.
Funny story: after a couple years at last big corp I worked for, I guess there was a decision made to join the ranks of the area's Best Places to Work. So memos were circulated, surveys were sent out and lo and behold, a year later the announcement was made: we had made the list of Best Places to Work, Large Company category. There was even a company-wide ceremony with a big cake to celebrate the feat.
So a few weeks later, I come across the actual dead-tree journal touting that year's Best Places to Work laying around in our breakroom. I open it up to find out where we actually ranked. Out of 44 companies in our category, #44.
We improved over the next couple years. Banners appeared around campus celebrating our achievement. The cakes got bigger. Things got worse for me personally at the company.
As you can probably guess, the impression I and others got was that the ranking was actually more important than actual employee sentiment. And I got the distinct sense that HR was motivated even moreso than previously for the sake of their Best Places ranking to push out employees that were critical (even legitimately, perhaps especially legitimately) of the way the company operated than deal constructively with their concerns.