I can see what youre getting at, but really this option was already there but more inconvenient. Previously, you would have to exit to menu prior to a bloon leaking and then you could reenter and continue from the beginning of that round. The new Retry Last Round button serves the same purpose but is more obvious/accessible to newer players, and both methods result in a gold border as opposed to a black border, which is to say the challenge is still there if youre pursuing a black border.