I Don't Understand Catfishes

Is there anyone that can explain to me what the draw is to being a Catfish? I recently found out that a friend of two years (not from here or EP) is not who "he" said "he" was. Due to a slip up on his part, I was able to get very solid proof about this too. Of course, she denies it, which I'm not surprised about.

So, what's the pay off? We were just friends. If this person were honest with me, I still would have been friends with her.

I just don't get it.