Dissociative Identity Disorder (DID) also known as Multiple Personality Disorder (MPD) was changed to such because as people have become more aware of what this disorder truly means - there have been some major changes.
When you hear the word personality you reflect upon the individual's actions, behavior, mood, etc. A patient with DID lacks one way of acting, they circulate throughout multiple personalities.
A reason for changing this is to highlight that the problem is not multiple personalities, it's the fact they do not possess a unified one.
Hope this helps!
