Because sometimes, the surprise "spoiler" ending is the only reason you'd pay $11 to see what is otherwise a turkey of a film.
Because sometimes, you vaguely remember an old movie that had some sort of plot twist at the end of it, but can't remember what it was.
Because sometimes, you're not interested in seeing that movie everyone's talking about but are dying to know what the hubbub is about anyway.
Because sometimes, your TiVo timer didn't get it quite right, and cut off the crucial final minutes of something that won't get shown again for six months.
Because sometimes, you fall asleep watching a mediocre rental, and would rather return it on time than pay two more bucks just to see the end.
Because sometimes, your trip ends before the in-flight movie does, and you really don't want to ask the pilot to circle the airport just so you can catch the finale.
And, let's be frank, because sometimes that guy in Marketing who's such a jerk to everyone needs to be put in his place...and how better than to ruin the ending of the movie he's been looking forward to seeing for the past three weeks?