How do I avoid this thing where all the cultures in my setting seem just like any other high fantasy culture?

I'm reading this book, which takes place in an imaginary world that's set over 50 years after a zombie apocalypse, and I'm realizing that this book is probably one of the first to explicitly explain how regional cultures would change over time based on the new environment. And I realized that I just tend to port over whatever mythos and supernatural beings I like from real-world cultures and merge them randomly. <br><br><br>So even after 50 years, there's always some kind of traditional coordinated style of dress for the people, which is pretty unrealistic seeing how fast regional dress styles change. Even when the people are spear-wielding savages, they'll still wear clothes that are reminiscent of the old world. Whenever I place a culture's mythology into my setting, it comes with all of the baggage of the real world. And I wish that I could avoid this problem, because I want to write a story taking place in the present day that takes place in a world that diverged from our own in 1800 and is now, in essence, a world with magic and dragons and shapeshifters and vampires and lots of other paranormal stuff, with me trying to create a world that is realistic and not like any high fantasy world. <br><br>So I guess what I'm asking is how to make region-specific and traditional styles of dress, cultural traditions, and mythologies change over time? How would regional styles change over time? And how do I make the changes look natural and not like a made-up culture? <br><br>The best example of what I want that I can think of right now is this book I'm reading. It frames the world as a place that went from modern society to a post-apocalyptic wasteland in a span of maybe ten or twenty years, and the book frames the catastrophic collapse of society as a kind of cultural reset, which is part of why I'm thinking of a similar cultural reset in my world. <br><br>Anyway, in the book, the world has somehow managed to accept this new reality over time, as coordinated regional styles of dress have formed based on the environment of their situation. One of the groups described is called the "Wasters", spear-wielding savages that live in the ruins of cities, and they have no coordinated style of dress; they wear whatever they find, even if it's not practical. In areas where there's no buildings left to scavenge from, people have begun to move from soft fabrics to hard leather tunics and leather pants, even if the tunic provides minimal protection, just because it provides more practicality and is more durable. People in the book have been trying to form larger communities and they've formed tribes, which I want to do in my world, and I'm wondering how I could make that work in my world.<br><br>So that's what I'm asking; how would I make these elements change over time? <br><br><br>Edit: I want to emphasize that I don't want to know how to create a fictional culture. What I want to know is how to make a real culture or traditional styles change over time based on environmental and cultural factors.