Blame Richard Pryor (who co-wrote the screenplay). ;’)
One of the gags the studio forced out in "Blazing Saddles" was that when the lights go out and Madeline Kahn says, "It's twue! It's twue!" the next line was supposed to be the sheriff saying, "Woman, get my elbow out of your mouth!"
Off topic, but in Animal House, when the float with Kennedy's head lands on top of the fire hydrant, the original gag was supposed to be a beer keg hitting him in the back of the head and going through. The studio nixed that.
Richard Pryor wrote most of the Mongo shtick. Mel Brooks was going to have him play Bart, but after seeing the comedy he wrote, he kept Pryor on as a writer. Brooks said his only real worry was the farting scene, which shows how much things have changed in the movies.
"Blazing Saddles" has been credited with singlehandedly killing the traditional American western. It offended just about every aspect of the genre, although some themes were trashed more than others.
I love the movie.