Why is it so hard for some people to apologise? They would rather pretend everything is okay and claim that they are not party to the fiasco in an effort to appear "cool". They even shift the blame on others instead of owning up to their mistake.
Sometimes all it takes is a simple statement like, "We apologise for the oversight" and then people can move on.
Unfortunately, when people are not willing to admit their mistakes, they do not learn from it.