A few reasons I can think of that may explain why:
* Older photos had more saturation
* Colour photography and screens were new and a novelty, so
it was pushed more to showcase their tech's capabilities
* Muted or monochrome colours by companies became the norm and associated with class (e.g., old rainbow apple logo vs newer monochrome logos), too much colour may be seen as kitschy
* Perhaps tied to the postmodern era as a differentiator, bright vibrant colours on products are seen as retro and/or cheap
* Also maybe tied to capitalism, vehicles, houses etc. with safe colours are better when it comes time to sell. I believe mass production would also result in more neutral colours
* With the ubiquity of cameras, more images of banal environments exist now
I wonder if another element could be improvements in resolution and quality as well, both on displays and in our fabrics/materials. Simplicity/flat design looks clean in high res screens and materials. It looks boring in low res screens and less fine materials.
* Older photos had more saturation
* Colour photography and screens were new and a novelty, so it was pushed more to showcase their tech's capabilities
* Muted or monochrome colours by companies became the norm and associated with class (e.g., old rainbow apple logo vs newer monochrome logos), too much colour may be seen as kitschy
* Perhaps tied to the postmodern era as a differentiator, bright vibrant colours on products are seen as retro and/or cheap
* Also maybe tied to capitalism, vehicles, houses etc. with safe colours are better when it comes time to sell. I believe mass production would also result in more neutral colours
* With the ubiquity of cameras, more images of banal environments exist now