Why do so many people confuse schizophrenia...?

with multiple personality disorder?

Because they're not educated?

Anyway, there's no such thing as multiple personality disorder anymore. So, why are you calling it that? It's called dissociative identity disorder now.

because it looks like that person has a different personality, but in fact, a person who is schizophrenic is just having delusions and the delusions they have are just like the ones if they will daydream (what they want in their mind).
Watch "A Beautiful Mind" movie.
It's because people don't read up on these two disorders. Experts for many years have been explaining that these two illnesses are different.
Because people aren't really familiar with mental disorders. For some reason, unless you're a professional or someone who has experienced it, either with someone or themselves, people don't want to know or associate themselves with it.
People have a hard time understanding mental diseases, as if it's bad luck or something. They just rather sum them up as "crazy people"...
My cousin was diagnosed with schizophrenia, that was my wake up call. I had heard of it but no clue of what exactly it was. I know now....
I don't know. I've seen that ever since I was an undergraduate in the early 1970s, and I've never understood why people keep referring to schizophrenia as "split personality." It may be the actual name (schizo - divided; phrenia - mind) that is the problem: "divided mind" sounds superficially like "split personality." The disorders are different, however.

A person with multiple personality disorder actually creates discrete personalities, usually with different names and occasionally with different gender(!), to segment aspects of their lives that would otherwise be unbearable. Abused children are most often the ones who create these "separate realities." One girl is a little vixen; one a little mouse.

Schizophrenia, on the other hand, is an emotional war within oneself. Different goals and needs, different attitudes; love/hate relationships within the family can cause it. The inner struggle is known; not blocked, the way it is in multiple personality disorder.

I used to wish I COULD create a separate personality to live in, to avoid the internal war. Never managed to get the sides separated enough to give them different names and build the "firewall" between them. Finally, other methods created a bridge over those troubled waters for me. Tantra is healing, my friends.
Because they didn't see "A Beautiful Mind."