Because if you swear without replacing some letters the automatic filter will first warn you and then kick or ban you. It is simply a way to bypass the filter.
You could always submit a ticket with proof (screenshot for example): http://www.chess.com/forum/view/help-support/how-to-send-in-a-support-ticket
Keep in mind that it is against TOS to name and shame people and can result in consequences for you.
Why do people have to always swear with numbers (Replacing letters for numbers) and spam useless an ddiscriminatory topics in chat? Once a guy called Zevurus_Znape used a racist term in main hall by replacing an i for _. Is there any way this can stop???