Why do this subs users change their usernames so much?

Sorry if I've missed something but I've seen so many threads with the same usernames and high karma counts. And they **all** seem to be comments of this one person, and I just can't remember that happening on other subs that I've been part of (although I admit it's not something that I pay close attention to)<br><br>Which brings me to my question, why do you change your username so much? (This is not me being mean, I'm genuinely **curious**)<br><br>Thanks in advance for the answers :)