There are various reasons why people decide to post anonymously. Some of them: - They don't want to draw too much attention. They like using the site, but they don't want to be a part of the people who form cliques. - They do so out of fear of being recognized. -paranoia- - Females ask and answer sexuality-related topics anonymously in order not to get messaged by males. - They see no reason to do so because they only want answers to 1 or 2 questions and then they leave the site. - They enjoy trolling (however, I think anyone can troll just as easily with their identity shown) - They fear judgment. - They like clicking the button. - They simply feel like it. - Anonymous feature makes you feel safe (r).
It varies from person to person. For me, I'll post anonymously when someone is requesting highly sensitive or personal information. If someone is essentially being nosey and their curiosity has evolved into something more intrusive, considering that I don't know them, I will most likely share my thoughts anonymously. It's no different from the human interactions that exist in real life. Would you be as willing and open to share a private story or experience of yours with some stranger you had known for less than 3 minutes? Same logic.
Other than that, if I've seen the user around GAG showing their a** and being verbally abusive for no legitimate reason, then I'm less likely to be interested in being too engaging or inviting with them thus the anonymous feature.
They are afraid of be confronted for their actions. This is why they tend to ask stupid questions. They are also embarassed, or the question is personal so they ask anonymously. But the most important reason of all: Because they can.