I've seen arguments claim that it's because the names have biblical meanings, however that doesn't make much sense. Just because a name has biblical meaning doesn't make it celestial in its origin. Angels have unique names unlike our own because they aren't human; they have their own language predating any form of human language, their names should be foreign and strange and something completely otherworldly and ethereal. It's not that hard to research the different kinds of angel names and their origins (of religious and cultural background) to see which one fits the character they want the name to portray. There are literally thousands of names to choose from, most of them androgynous and all of them incredibly beautiful.
I don't know. It's just something that's been bugging me for a while.