I perused one Disney forum and came away with a plethora of reasons why the villains garner so much attention:
But one reason why villains are so popular, is because they are often the main reason a story even gets told: no heroes and no conflict without villains. Besides, villains can be more colorful and exaggerated than the heroes. Heroes always have to be good and wholesome, while villains can do as they please. That makes them popular.
Heroes/Heroines are generally bland, blue-eyed characters with the same or similar back-story. (Orphaned or death of parent, lost and alone in the world, pathetically too cute to not feel sorry for…) You get the picture.
In contrast the Villains (usually) look very different from each other and their histories are rarely known. (We just assume they were always EVIL, right? NAW!) This makes them popular with fans because they/we like to know about how our favorite Villains came to be; whether it’s by researching the heck out of the original fairytale or by creating our own fantasies in art and fiction.
I think it’s mostly the fact that villains are given the room to be more dramatic, outrageous, or (over)emotional than most other Disney characters. Scenes of the Evil Queen watching SW’s death or Cruella becoming completely maniacal come to mind. Of course, not all villains are that way (Shan-Yu and Tremaine, for example, are mostly cold, calculated characters), but regardless their villains delve into the depths of humanity far more than their heroes do (for the most part). They are able to terrify (as with something non-human like Monstro), or display a certain–very real–obsceneness [sic] that people meet, perhaps experience, in their own lives (extreme bitterness, jealousy, racism, greed, selfishness, murderous desires, etc.). And, to focus on the advantages specific to animation in evoking a mood of evil, you get incredible scenes like Ursula seizing Ariel’s voice (Ursula’s tentacles themselves are something done to a menacing/captivating effect that couldn’t be recreated as successfully in live-action) or Maleficent’s mesmerizing of Aurora. Some people have criticized them for being what you might call flat or cookie cutter (in other words, they are less “characters,” and more plot devices that drive the protagonist’s story). But the lack of background information often gives them a certain mystique, a power to command their audience. They are often very basic in their motivation, to the point that they become almost primal.
So, I guess, the simplest way to put it is: They put on one hell of a good show.
And that’s what it really boils down to, isn’t it? The villains put on the best show — and they make the fantasy world go round. Without great villains, Cinderella would have never tried on the glass slipper, Wendy and her brothers would never have learned heroism in Neverland, and Giselle would have never made it to New York City to meet her true love, Robert. Without the bad guys we don’t realize who the good guys really are and how we can aspire to be one ourselves.