maybe they havent figured it out because there are many different normal mental and physical health problems where a person can have as you say "2 of me"

this is what happened to a friend of mine who kept thinking they had DID. they kept telling their treatment provider "there are 2 of me" and when answering questions answered things like "yes there are 2 of me when this or that happens it feels like I switch into two different me's".... come to find out the person had ADD/ADHD which comes with sometimes perceiving herself as being two different types of personality. one happy go lucky everything is dandy and the switch into being anxious, sometimes reserved sometimes obnoxious and other problems.

another person I know who thought they had DID turned out they had brain cancer..

I could go on and on but the short of it is that there are many different things that can cause this problem.

my treatment providers have the same problem with me sometimes where I have a problem but because I have so many different normal, physical, mental and medication problems all they can do is find the one that......best fits...according to all the tests and such.

since all the tests and such are not diagnosing your "2 of me" as DID maybe you can sit down with your treatment provider and give them more information about what you mean when you say there are "2 of me" then they can explain to you how and why they see you diagnosed the way you are. it might just be a communication problem where they need to hear it from you verbally in more detail based on whats happening with in you. some times even just the 5 minute conversation doesnt do it with my treatment providers and after I go into great detail about what I mean when I say something then they get it right.