The primary role of commentators in anything is to keep the viewers at home entertained in the way that they talk about the game. Super analytical commentary without some kind of humor or hype thrown in the middle is boring, and overly hype commentary about next to nothing comes off as awkward.
Because of this, commentators tactfully choose what to talk about and refer to it in a manner that keeps the viewers at home as entertained as possible.
Some of the easier jokes regarding the professional Smash Wii U community right now all revolve around Tamim "Mistake" Omary. There's no saying what made him want to be known as "Mistake," but it provides a lot of opportunities for bad puns.
However, commentators have to be careful while making bad jokes on the mic. You never know what will happen if you make Calvin "GimR" Lofton mad. In this case, he turned on his own mic and informed the commentators that letting them on the mic was a mistake.
As Reddit and Twitch chat would say, The GimZ always winZ.