^^^Well, honestly... how much are roman numerals used these days? Greek or Macedonian letters? Early Germanic runes?
Yes, it's NICE to know these things, and definitely rewarding/interesting from a historical perspective... but for 80% of society, it's simply not worth the effort if there's no use for them. And on a grand scale there just isn't a large use for them. Unless you're in the habit of naming your pets Phillip XVI and Phillip XVII, etc etc.
Besides, everyone has different interests. To say that someone is ignorant or lacking because they're not interested in HISTORY (and that's what roman numerals are) is just rude and incorrect. I know them because I'm a history major, but most people will never encounter a situation in which they need to know roman numerals.
There's nothing wrong with that. It's just how the world goes. Old number systems and languages fade to be replaced by new languages and number systems... there's nothing wrong with societies adapting to modern changes in language and syntax.