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But he (Cuaron) also brought in the Muggle clothing, which is actors said they liked.
That's a wrong assumption. J.K.Rowling brought muggle clothing into the books. Check if you don't believe me. The kids never wear their uniforms out of class. Period. So why should they in the films?!
The reason why muggle clothes are prominent in PoA is simple - PS/CoS had more class scenes. Plus they had the kids in robes in times when they shouldn't have been - no kid wears school uniforms when they don't have to yet in PS they were wearing their school robes even when they didn't have to! How unreal!
It's just that in PoA, there were less class scenes so less robes. Honestly, would you wear your uniform on the weekend/after class? Of course you wouldn't and neither do they both, in canon and in the films.