well, it's an entirely client side thing to have, so the "why" very much comes down to the developers balance on adding extra code for extra convenience. The developer might like it personally, or they might find it's a feature that their users want, or both.
As an example, I have my thinkpads prtscr button hooked up to automatically capture the screen, upload to 0x0.st, put the url into my clipboard, and then alert dunst to pop a notification that it's done.
It takes a very common 60 second process and makes it almost as fast as prtscr, ctrl+v
