From what I read, it's a case of "can't do it the right way originally because of patents/legal/whatever; can't change it to the right way ever since because th

From what I read, it's a case of "can't do it the right way originally because of patents/legal/whatever; can't change it to the right way ever since because then every airbus pilot would need to requalify, every book rewritten, etc ...". Sounds like a terrible case of rotten legacy support.