Is this a form of deux ex machina that we are so used to as viewers that we don’t even blink? Or is it one of those predictable things that must happen in movies? Or maybe it’s got something to do with psychology — a person may feel the need to explain why he or she is doing something.
Whatever the reason, in some movies this is a plot element that is grating. It does work in some movies but it does seem like an overused element. The flip side is that if villains didn’t gloat you’d never have series like James Bond that span decades.
I’m reminded though of a scene from The Good, The Bad, and The Ugly, where Eli Wallach’s character (Tuco, aka Ugly) is in a bathtub and someone comes in and points a gun at him but doesn’t shoot. Here’s the dialogue from Wikiquote:
One Armed Man: I’ve been looking for you for 8 months. Whenever I should have had a gun in my right hand, I thought of you. Now I find you in exactly the position that suits me. I had lots of time to learn to shoot with my left.
[Tuco kills him with a hidden gun]
Tuco: When you have to shoot, shoot, don’t talk.
If movie villains heeded Tuco’s advice, my feeling is that doing this would tighten a story / script where the gloating was used as a plot device to help the writer resolve a situation.
Tighter movie = better experience for viewer.