Why was the Windows File Transfer so bad at predicting transfer time?

The funny thing is that moving and copying files got EVEN WORSE in Vista. And when they made things worse than XP, it stayed that way even with Metro, but now it's a more elaborately decorated form of even-worse-than-before.

In Vista, suddenly, even just to move a 1KB plain text file from the Desktop to the Documents folder, you might suffer a wait time of 15 to 30 seconds. God knows why.

Perhaps you just saved a 30KB JPEG file to your downloads folder, but now you'd like to drag and drop it into your My Pictures folder. Guess what? You just earned yourself 12 seconds of indeterminate progress bar. And no one can tell you why.

With Vista, came the belief that it is necessary to present the user with an indeterminate progress bar for no less than 5 seconds, if they ask to go to the bathroom. Is it User Account Control? Is it because of disk I/O wait time, when writing to the event log? Is it because checking system policies? Is it because of graphics rendering overhead? Is it because we have to wait for a programming bug to trigger an infinite loop exception?

No one knows.

But, even in Windows 7 and Windows 8, animated, flashing progress bars everywhere, probably because User Interface Design.

Silly answers to the question. The answers basically apologize for the choice to show a time estimate.

because of 'sliding windows'. (pun intended)