Freeing up space · Stopping, undoing and apps in the way
Why doesn't the Stop button end a clear-up immediately?
Short answer: It finishes the folder already in progress so nothing is left half-removed, then halts. The screen explains what it's doing during that short gap.
Because it finishes the folder it's already working on before halting, so nothing is ever left half-removed. That leaves a short gap between pressing Stop and the work actually ending.
During that gap the screen says what it's doing, so you aren't left wondering whether the button worked. A Stop that looks like it did nothing would be worse than one that takes a moment and explains itself. See what Carry on does.