Good vs. Evil is a storytelling theme as old as time, and it's one that shows up in the vast majority of Hollywood films. It's an easy concept to shape any story around. Audiences can simply cheer the good guys and root against the bad guys until those credits roll. Any moral gray area is usually small enough to fit inside a bread box.
But sometimes it's not that simple. Sometimes, because of or in spite of the filmmaker's intentions, you find yourself cheering on the bad guy because...well, they're just too damn likable.
Maybe you don't necessarily agree with their end goal of world domination/mass murder/etc, but you still appreciate the cut of their jib. Beneath that ostensibly evil shell, there's something incredibly endearing about them.
Or sometimes they're just sympathetic souls who've been dealt a terrible hand in life, and have been driven to do some less than savory things. Either way, there's something wonderful about understanding that the antagonist is, at least on paper, supposed to be a terrible person, but still being able to respond to their behavior with a smile.