Reddit mentions of Blue Jeans: The Art of the Ordinary

My university has been running a project for a few years now, led by Professor Danny Miller, entitled The Global Denim Project and its aim is understand the phenomenon of denim, its enduring presence in global fashion and how different cultures interact with the fabric on a day-to-day basis. It's a really cool project, so check it out! It's got links to other projects related to denim as well.

For those with access to a university network, here is the original paper that inspired the project. For those who cannot see more than the abstract, the project page linked above provides a good synopsis.

It accompanies the book he wrote on the subject, Blue Jeans: The Art of the Ordinary if anyone is interested in that, too.

I'm sorry that I cannot directly answer your question, I feel it is perhaps a lot more multi-faceted that we think, but I hope that the links above can point you in the right direct and may be of interest!

Edit: I realise that the links I have provided, and the approaches discussed in them, are anthropological rather than historical so not directly helpful for OP. That said, the question itself relies more on anthropology than history. There isn't a singular narrative or specific cause as to why we see denim in every country throughout the world and have done for decades. It's the result of numerous cultures interacting over time.