Flash storage might be the highest-margin component sold by Apple, so there's a conflict of interest with filesystem features that reduce the need for storage.
That is mostly limited to copying photos and videos to/from the "Photo Roll".
There are many thousands of applications which process other file formats. Some of them have natively implemented support for a 3rd-party (expensive) storage device called iXpand, which itself comes with a poorly implemented app. These third-party applications are poorly and pointlessly (re) implementing basic OS file system I/O functions.
Is it possible that these pointless I/O hoops are hampering uptake of $1000 iPad Pros for "laptop" use cases?