I have a reason why people would want to create alternate accounts that is more valid then any of the above reasons: someone spends a lot of time calling out scammers and stopping scams. As a result scammers don't like him (it would probably be more accurate to say scammers would hate such a person).

A person who spends a lot of time weeding out scammers probably would not want their RL identity associated with their account because scammers would probably try to associate their RL identity with a bunch of BS illegal shit that is not true (just look at Vod - I am fairly confident that he thoroughly regrets associating his RL identity with his account now).

If such a person wanted to trade with people they would likely do so with alt accounts in order to protect their identity.