Why are most Western cultures materialist? They take Methodological Naturalism as some kind of baseline, which is a fallacy.
Why is this?
The accidents of history, I'd guess. The success of "natural philosophy" was due to the success of one school of Roman Catholic thought, which takes us back to the dawn of the Renaissance, Paris in the time of the Schoolmen, the exploration of Greek texts that had survived in Arab culture, and Aquinas' daring and influential ideas that it was not enough to read that God exists, it must be shown by reason.
That strain of enquiry continued to exist in the West despite various challenges from various clerics, until it turned into the Enlightenment, whose most famous natural philosopher was Newton, famous as a genius and as a dingbat. Shortly we have the Germans boldly exposing the bible to critical analysis and arguing for Markan priority before 1800. At the same time, discoveries in geology were contradicting biblical accounts of the Creation, the Flood &c, giving rise to the tensions that ran through the 19th century, particularly in western Europe. The acceptance of evolution as the origin of species following Darwin's publication 1859 was also part of the decline of religious and biblical authority among many of the educated, including eg Anglican theologian and bishop John Colenso.
What had happened was the removal of authority from the bible as the explanation of the earth and of its creatures, and the passing of that authority to those who instead drew their conclusions by inspecting and seeking to explain nature directly. Meanwhile inventions, not least the railway, were changing the psychology of city and country and challenging regionality / parochialism as the best and brightest made their way as never before to the centers of business and of learning, Steamships brought Britain closer to Europe, and to the exchange of ideas.
In the 20th century, WW1 thoroughly changed not just the politics, but the nature of politics, in Europe, with women in the workforce, votes for women in the UK, the formation of trade unions and the formalization of them v us, and the rise of primitive socialism. WW2 caused a worldwide breaking and remaking of the world order, in Europe, Asia and the Pacific.
And with the growth of technology, TV arrived, the first nail in the coffin of public assembly for church, Lions, Rotary, and much more. The cell phone hastened that process, since it was no longer necessary to be in someone's physical company to talk to them and know what they were doing. This has much reduced the influence of the old centers of authority ─ the expert, the politician, the newspaper editor, the clergy ─ and replaced it with alternatives, some of them capable of generating chaos.
If you want religion, you can take your pick of a huge variety. But if you don't want religion, these days no stigma attaches, no tithes are involved, you can play golf / stay drunk / go hiking / visit the library / watch movies / party / &c all weekend.
Something along those lines is part of the answer to your question, I think.