I'm pretty sure it's because people who do that are not very educated
You mean Brits and Americans? Yeah, people who can't accept logic or the metric system don't come off as very educated. Face it, you handful of English-speaking countries simply have nonsensical conventions that now only seem "natural" to you because you've lived with them all your lives. To the rest of the world, writing is clear and intuitive, in that:
"one kilometer" = "1 km"
"five milligrams" = "5 mg"
"ten megabytes" = "10 MB"
"fifteen euros" = "15 €"
But no, screw logic 'cos we're 'murricanz and 'murricanz know best, so you went with:
"twenty dollars" = "$20" (?!?!?)
Not to mention the rest of your screwed up ways of measuring and formatting things...
In general, it's better if you simply don't bring these things up at all. Just stay appropriately silent and ashamed.
I prefer year-month-day. It sorts better.