I think the biggest problem is simply that it was a software bug that occured infrequently enough. To change a working piece of software that has thousands if n

I think the biggest problem is simply that it was a software bug that occured infrequently enough. To change a working piece of software that has thousands if not millions of problem free flying hours behind it is not something you do "just because". It requires lots of analysis and testing to make sure that they don't introduce new problems.