Because outside the little western bubble it might be understood more accurately along the lines of self defense, or a response to aggression and political interference motivated by any shady bullshit from proxy wars to controlling oil supply.
Because "weapons of mass destruction" definitely deserves the quotes and was used for a similar purpose.
But mostly because giving something scary a name that abstracts away everything except that it's scary not only makes it super easy to sell publicly, but also makes it super easy to aim the public response to said fear at whatever the label can be twisted into applying to.