The other point about parodies is that they often focus on the original song in a negative way, they take the original work and laugh and ridicule it.
let us use somebody elses work to get a cheap laugh, what happens next is that when a performer sings the original work, members of the audience will possibly be thinking about the parody while the original is being performed.
The Kipper Family[ who parodied The Coppers were very good perfomers, but when I hear other perfomers doing these parodies the performance is often mediocre , there is rarely an explanation about the original copper family or even who the kippers were.