It's because if you changed your name after joining, people would get confused. If you where sparklehearts one minute, and another username the next, no-one would know who you were! Also, if you had 23 graphics with your username on them (which some people do - or more!), then you would have to re-create them and waste half an hour of your life uploading them to the internet. So, the awnswer to your question is that, you cannot change your username for the benifit of not only every other player, but yourself too. Besides, with such a pretty name like sparklehearts, I'm suprised you would even think about changing your name! So be grateful for what you have and what others don't, that's what I always say. Have a wonderful day, sweetie! ;)