I think most of you are missing the point.
Yes, creating the cancel button is easy programming. Other similar games have it.
Yes, making the loss of coin or mats would prevent abuse.
However, not having the cancel button makes people think about using the speed-up / instant finsh, which costs T-cash, and that is the end goal of the game right? Making us spend T-cash, and buying more with real cash?
THAT is why there is and won't be a cancel button.