According to Wikipedia the two variants exist because the digits of large numbers used to be grouped into groups of six digits but in order to improve readability this was eventually changed to groups of three digits and some insisted that with that also the naming should be adjusted. A long scale trillion has three digit groups when using groups of six digits (1,000000,000000,000000) and six after the switch to groups of three (1,000,000,000,000,000,000) which then should be a short scale sextillion but somehow it ended up as a quintillion.
So basically
I'm sorry it had to be done https://www.youtube.com/watch?v=rIB5HEcZBs8
N-illion = 1000^(n-1)
Isn't it more like:
Since the OP was saying groupings use to be by 6-digits, not 3-digits (i.e. "1,000") as seen today.The original long scale makes more sense, billion, bi million, twice six digits.
Yet, mille and milli- mean thousand.
But the suffix -one in Italian is used to indicate something big - spaghetti vs spaghettoni - so a milione is a big thousand, a million.
Thanks!
This is the key piece of information for making sense of it. Ultimately the OP's insight is that the number-naming system used in the west is thousands based instead of millions based, but came to that by observing the number-naming outcomes instead of the source notation that led to it.