With Roman numerals, position is everything. IX is different from XI.
With Roman numerals (and the Greek system that inspired it), numerals require a smaller character set than most alphabets, and they are positional.
You can define an entire alphabet with 3 characters if you do it with Roman numerals. But how do you hide the fact that it's Roman numerals, which everyone knows? Make some of them look like letters or abbreviations, add a few nulls, voila! They look like text.
With Roman numerals (and the Greek system that inspired it), numerals require a smaller character set than most alphabets, and they are positional.
You can define an entire alphabet with 3 characters if you do it with Roman numerals. But how do you hide the fact that it's Roman numerals, which everyone knows? Make some of them look like letters or abbreviations, add a few nulls, voila! They look like text.