Endings don't happen in real life. It all just keeps on going. No certainty in bad ends. TERRIBLE ends are no good, but Good ends are irritating and leave you with a saccharin aftertaste. A bittersweet ending is more realistic, and gives continuity to make it seem like it's just a snapshot of a moment in time rather than a bubble universe that's come to an end suddenly.
I think I phrased that right. And this is just an opinion.