Your claim that no operating systems support this seems extremely unlikely. I’m pretty much certain there are multiple Linux desktop environments that support vector based background images.
Well, I had assumed none had support since none of the OSes I use regularly had support. I stand corrected.
That said, I do still wonder why none of the OSes that I use (Windows, MacOS, Android, iOS, accounting for pretty much 100% of the OSes regular people use) have support for it.