Why didn't they stay true? Spoiler

Changing to Oregon feels like a natural progression, since they've changed most of the characters' backstories (Norman's dad was supposed to have died when he was still a kid, the whole family was supposed to have been living in the house for years, etc). Norma's death, I think, is even more tragic the way it happened. Not to mention that Norman himself has gotten quite a lot of hate for killing her the way he did, in an attempt to end both his and her misery in a quick and painless way. Can you imagine the vitriol he'd get if he did in it a fit of rage?

If they really had to stay "true" to the movie, there would be no Dylan, possibly no Emma, and no Romero. Norma would be largely unsympathetic and her "lover" would be a shady, nondescript businessman by the name of Joe Considine. Of course, Norman would poison them both by putting Strychnine in their tea.

Are you sure you would have preferred that?

The most important elements of Psycho/Bates Motel up to this point are Norman's mental illness (DID), his abnormally close and twisted relationship with Norma (which also manifests in his illness), and her dying and his continuing as if she were alive as a way of coping with her absence. Anything else can be altered while retaining these basic facets.

The place of residence and the mode of Norma's death are not particularly important in the grand scheme of things.

From the very 1st episode, it was clear this wouldn't be canon to the movies. It takes place in present day, after all.

I like Bates Motel differs from original Psycho. I have enjoyed this series so much and for me I like when there are a little variety compared to original show.