Because MTP is utter rubbish.
Really, people complain about iTunes? It's never failed me as slow as it is. Try using MTP...
I mean, the expected workflow is: I hook up the device to the computer, it shows up as a storage medium in my system. I can move files between the device and my computer as if it was an external disk or USB drive.
Anything on top of that is designed to be annoying.