At the $bigcorp level, they ask survey panels "Which of these interfaces looks more modern to you?" that's largely the extent of the justification to completely

At the $bigcorp level, they ask survey panels "Which of these interfaces looks more modern to you?" that's largely the extent of the justification to completely change the entire UI that has been perfected and beloved by users over many years. The users begrudgingly learn the new UI, and a bunch of project managers get promoted and leave for the next company to do the same thing.