Question: Newbie question on simplify

I am new to Maple. I'm having trouble with simple caluclations such as the one in the image. The answer (after simplificatoin and cancellations) should be (|a|^2+|b|^2)(x^2 + y^2 + z^2)  but it's not happening! The result shown is correct; only the simplification is missing. What step am I missing?

The calculation is so simple, a look at the picture should suffice for the expert,

(sorry! I still don't know how to pick-off a single tab out from the whole workbook).

Question-2: judging from the missing overbar (complex conj) on z, the "assuming" seems to only apply to z and not x and y.

if that is correct, then why?

Question-3: How can I implement the constraint (|a|^2+|b|^2)=1 (preferably)before or after this  multiplication? I tried assume((|a|^2+|b|^2)=1), and though it compiled it did not help with the simplification.

TYVM