[Gigachad]

I feel like the reason for the change in design trends was that for most of human history, ornate details and complexity required immense labour and signified wealth.

Then with modern technology, we could print or weave any pattern you want on fabric effortlessly. Instead of a stone mason chiseling away all day, you can pour plaster in a mould and have all that same detail.

Now that detail is cheap, simplicity is on trend.

[robertlagrant]

You're right, although once something isn't impressive to do it converts to a fashion-related trend. Fashion doesn't often have a practical benefit, so a lot of it is just "I want my stuff to look different to my parents' stuff, and that makes fashion cycles, where people's fashionable floral wallpaper now isn't too different from what their grandparents had.