Just my personal speculation, although I think it fits the history:
Remember CB radio? EVERYbody on CB had to have "a handle". (How THAT started, Clinton, I don't know and don't care mightily, although it just might have come as a transplant from ham radio.)
When the net and the web came along, I think the same people who had been CBers became denizens of the new medium(s), and brought that in-group habit with them.