Back in the day you could choose whatever username you wanted, and it had a lot more meaning than a display name that could be changed at a whim. Nowadays, your username is something like outtawhack2356 and good luck getting anything much recognizable.
Maybe it's no big deal, just set your nickname to whatever you want and ignore the username. If more people recognize your nickname you might be less likely to change it.
Still, there's not the kind of tight binding from username to user like I remember. Nobody says "yeah, that outtawhack2356, he's a real funny guy".