The need for the explanation is because an AI can learn to discriminate against protected classes even if they aren't explicitly part of the dataset. You might not have included race in the inputs, but you did include their name, and it figures out that people named "Jakub" should be declined for a loan. The AI can't say that it's because they are Polish, but it learned to discriminate against Polish sounding names because of all the racism in the training data. We could uncover that if the AI was able to explain that it denied the loan mostly because of the name, and that the other pieces Y and Z did not factor into the decision as heavily. Just saying X Y and Z doesn't help us figure out which of those pieces are the important parts for denying a loan.