I've noticed a whole lot of people confuse schizophrenia with multiple personality disorder. Two completely different conditions. Why?

I was going to say Hollywood and remembered reading some definite treatise to the effect, but of course when I went looking for it, couldn't find it. Instead, there's this very technical explanation:
"Because it portrays images that are always seen as being external to the character, together with thoughts and ideas that in reality are internal, the cinema helps to further exacerbate the confusion. Thus, it becomes very difficult to distinguish a split personality from a hallucination because the visual nature of the cinema requires that both DID and schizophrenia must be shown as something external, tangible, and visible to the spectator. Resources such as using two parts played by different actors or conversations between two different personalities kindle doubt in the spectator as to whether what he or she is seeing really exists or is merely a visual representation of a mental process. This is a key point since it determines whether there are hallucinations or not." http://revistamedicinacine.usal.es/en/volumes/volume2/num4/998
Though, in real life, the two aren't always easy to tell apart either as discussed for example in https://www.ncbi.nlm.nih.gov/pubmed/18652789 "However, substantial data exist to document the elevated occurrence of psychotic symptoms in DID; awareness of these features is necessary to prevent diagnostic confusion."