That's easy to say for a file picker on desktop OSs, but what happens when you need to layout a page on all 3 desktop plus Android and iOS?
Do you need to design 5 designs that include 5 different buttons, 5 ways of navigating through the app, 5 different sets of icons, 5 different styles of animation, etc...
Hell even with a file picker, what happens when you use it on a platform that doesn't really have the concept of "files" like iOS or up to recently Android (at least in what is normally exposed to the user)
Roll in various versions of each OS and you are up to needing 10+ ways of doing most things. How are you supposed to create anything even remotely complicated?
Do you need to design 5 designs that include 5 different buttons, 5 ways of navigating through the app, 5 different sets of icons, 5 different styles of animation, etc...
Hell even with a file picker, what happens when you use it on a platform that doesn't really have the concept of "files" like iOS or up to recently Android (at least in what is normally exposed to the user)
Roll in various versions of each OS and you are up to needing 10+ ways of doing most things. How are you supposed to create anything even remotely complicated?