I think popular entertainment is a reflection of the times. The '70s film was pretty fatalistic, with lots of exaggerated violence and a projection, cities being dysfunctional and in decline, and traditional values being lost. Romantic comedy? Not so much. Tearjerkers instead. America was in the doldrums in the '70s economically and culturally so it fit the mood.
The '80s flipped it, very upbeat with lots of openly patriotic themes, the violence was made more cartoonish bright colors, bouncy music. Light romantic comedy was back on the menu. The national mood was positive (leftists were miserable, of course. They always are. But they were in retreat then).
The '90s was eclectic but there were several films that featured a 'nothing is what it seems' sort of vibe. For example The Matrix, Seven, Usual Suspects, Sixth Sense, Groundhog Day, The Truman Show. I'm not sure what that says about the zeitgeist of the era though. The effect of widespread internet access?
The last 20 years has been post-apocalyptic / zombies and superheroes everywhere. Zombies = a force of nature, the uncontrollable threat. You can't defeat the zombies anymore than you can stop a hurricane. That's never the point, its just to survive and so they are really movies about characters under extreme pressure and how some rise and some descend to the depths of human nature. Different takes on that, sometimes humanity bonds together to fight back and the threat unifies people (World War Z). Others like the Walking Dead seem to basically say that man's default is aggression, selfishness, and oppression with just a few willing to fight for the values they held before the zombies came. I tend to think zombies are used as an avatar for climate change by hollywood writers (maybe on a subconscious level, reflecting their general anxiety that the world is sitting on a knife edge).
But you know, you could name 100 exceptions to every point I made, it's just some random thoughts on the intersection of pop culture and national mood that I've had over time.
I forgot to mention that zombies are not just reflective of climate anxiety but also maybe the threat of faceless random terrorism (post 9/11).
Perhaps it is a pessimistic and dark reflection but IMHO this fascination with vampires, the walking dead and malevolent spirits reflects how American culture itself has devolved over the last sixty years. Significant segments of the population have embraced drug use, abortion, homosexuality and all its perverse permutations, mindless dependency, child exploitation and abuse, miseducation and tolerance of all sorts of bizarre harmful behavior. Neo pagan earth and celerity worship has replaced traditional religion for many. Therefore Hollywood, which is at the core and reflects this decadence, makes movies and shows that feature these death themes.