Compared to people who are unhappy, people who have good experience post about it at a much, much, much lower rate.
Its the same for product reviews. There are a lot of products with mediocre reviews because people who actually bother to write a review most often have complaints.
Statistically speaking, if you look at the total number of Amazon SDEs, and consider the fact that Amazon still makes a shitload of money in all their sectors, that means that majority of the people have no issues working there. If it was across the board bad, people would go to other places, which would directly results in declining profits and growth of competitors.
