Neither do the other thousands or millions of people who do so, but it’s not a particularly uncommon thing and it’s likely enough that (birthdate) is the reason it’s there. I’ve got my birth year (not '88) in my username for some sites because the bare username was already taken
If you look a bit around in this thread, someone linked an article that mentions he was born in 1988.
How convenient.
He didn’t have to put it in his username.
Neither do the other thousands or millions of people who do so, but it’s not a particularly uncommon thing and it’s likely enough that (birthdate) is the reason it’s there. I’ve got my birth year (not '88) in my username for some sites because the bare username was already taken