I would guess because they want to have a sock that has the same interests/fandoms as themselves but don’t want to deal with people like OP exposing them for it. Also like others gave said, it is just RPing. If this was real life I would question the amount of effort needed, but switching accounts online just to maintain a fake identity is the lowest/most tame level of catfishing. If they were having anon discussions, “both” identities were on a live chat at the same time, or whatever I would be like o.O