Maybe that's because Japanese does not distinguish between V and B phonetics. A lot of languages that use both letters don't distinguish them either, spanish being one of my languages, I know that SOME regions in Spain pronounce V with an F friction, but the language rules don't distinguish them, other than changing the meaning of the word if you use one or the other (ex:
vaca/
baca). The same could be said of Motabia / Motavia, even if at that time we didn't know the pronunciation, the japanese name would be with a BI because they don't have any other choice.
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