For me I feel like anonymity is often there because someone has something to hide. Perhaps a bad reputation as an RPer, or former failures as a mod.
At the same time I see how people would like it so that they don't have to get involved with OOC trivialities. Those are the people who just want to write and avoid OOC BS that can sometimes get in the way. I can see the benefits of both, but I personally am not comfortable in anonymous games.