Probably because some people tend to pick user names that identify them in some way. Take me for example, I have a few names I go by but this username is definitely helpful in identifying me. I use it on the other place, a couple of emails, discord, telegram, etc. I don’t feel the need to be as anon as possible (no shade on those who do) so I main this one. I have a few others that I have been known to use and those are mainly for things that I don’t want easily connected back to me.