To try and answer the question from a literary standpoint: fairytales and fables have several elements that make them ideal for melodramatic development, especially in a commercial setting.
One is that of 'archetype', which the article here touches upon. Another is that of typical or 'structured' conflict, which this article delves into somewhat more.
You see them working less successfully in standard drama, because the dramatist has to 'bend' the audiences' expectations -- for 'surprise', for character development, for art.
In standard drama, the story must project itself, not be propelled by customary, 'established' factors.
BTW, the very best opera also does this.