On the other hand, I think short-scale millions and billions are used far more often than the larger numbers, and the starts of words tend to be more salient th

On the other hand, I think short-scale millions and billions are used far more often than the larger numbers, and the starts of words tend to be more salient than the ends, so it's useful to have them distinguished by the first letter instead of the last syllable. (Plus, "milliard, with an 'ard'" doesn't have the same ring to it.)