Why was "dissociative identity disorder" NOT recognized as a mental disorder that could excuse criminal responsibility?

I did some research and it’s clearly the case the courts have rejected the admissibility of DID evidence. Especially since State v Milligan (1978). Especially in the UK, for insanity defense at least. Occasionally in the USA this defense has been succesful. But that’s just that. Occasionally. I mean, we’re in 2020 and we still don’t recognize DID as a defense for criminal defense? That’s outrageous!