Part of the reason these types of nouns are chosen is that sharp, shifting sounds are easy to recognize without much manipulation. If you call your assistant Anna or Beau, you will have to filter out more false positives.
Of course, marketing takes a beating, too, because no one wants to shout “Hey Ziktroxier” no matter how popular that name is, but a cute, round human name like “Google” can be tricky at times.
Plus, you’re stuck with the fact that everyone should pronounce the name roughly the same way, unless you want to do the local processing for each region and dialect manually. Alexa and Bixby are a combination of simple voices that you will find in many languages. However, it will be difficult for the Englishman to pronounce “hee Jochem” clearly, and vice versa. “Siri” is indeed a somewhat striking choice in this regard since there are as many ways to pronounce r as there are in languages, although the primary focus at the time was of course only on American English.
Cortana in English worked well in my short experience with it, but you had to open a whole bunch of data channels to Redmont for it to work. It wasn’t much different from Google’s Arts Assistant, really, although Cortana had the disadvantage of getting less information about me than my existing Google Assistant account.
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