[Nasrudith]

I think the reason pessimists carry the day for legitimate reasons is simple - those promising sunshine and rainbows tend to be the same one's picking your pocket or try to turn you into a puppet to be disposed of when no longer useful. Another of pessimism's virtues is that it breeds preparation. Unlike cynicism it can persistently endure pleasant surprises as well.

The reasons for dominance of pessimism culturally are also cynical - negative campaigning tends to work well and it is easier to find something disliked by many diverse subfactions than something unclaimed and liked by many. Plus it is easy to tear down compared to building something.

Hollywood's lack of science optimism has another obvious reason aside from anger at being disrupted by competition from newer technology. It requires far more creativity to come up with something plausible, optimistic, and having a problem that you can hang a plot and spectacle upon than making some shallow nonsensical dystopia which makes as much sense as using nuclear fusion reactor powered robots with energy weaponry are used as overseers for coal miners with pickaxes. Which leads into my next point. What has generally been a death knell for darker aesthetics and genres is inability to be taken seriously anymore; whether by overexposure with a lack of variety and/or a biting parody. It probably affects them worse because there are far more ways to make a "neutral" genre like say Western, than a darker one say a slasher film - the emotional ranges are inherently more limited by definition.