Perhaps a fresh pair of eyes is always going to notice a bunch of potential changes, which would improve things from their subjective point of view. But humans are notoriously bad at absolute scales (see Thinking Fast and Slow by Daniel Kahneman) so it's hard for us to decide "I can see a bunch of issues but they're all below the threshold for changing". The top of the scale is always what is most important out whatever issues are left. Adding the duck reshapes the scale so all those other things seem (correctly) trivial in comparison.
To put it another way, if the deadline is tight and the program kept crashing, maybe they wouldn't have even asked to remove the duck! The scale would have changed again, and the bit with the duck on it would have been compressed below the threshold.