[Opinions] Because different countries have different accents and phonetic rules
I'm from the middle of the U.S. and I pronounce Sara and Sarah exactly the same, but they are both SAIR-uh.
Norah/Nora and Susannah/Susanna are a different case, because the rules really only apply when you have the letter set "ara" in a name (Tara, Cara, etc).
Oh, I pronounce Hanna and Hannah as HAN-uh, though Hana is HAH-nuh.