Some people just like to complain and unfortunately, they are more likely to log on and make it public.
When I worked the hotel front desk, I never once saw a fellow co-worker behave rudely to a guest, and anything that did go wrong was completely out of our control. Sadly, that didn't stop people from posting terrible reviews online, while neglecting to mention the lengths that we would go to trying to improve the quality of their stay.
My favorite complaint? "Children were making noise in the pool area!"
Those terrible kids, having fun and splashing in our pool! Don't they know that a pool is like a library? Shame on them!