Why do we not use Roman Numerals a lot these days.Thank you Regards, Aarav Mishra?

Answer 1

It's somewhat tautological, but one reason we don't use them is because nobody uses them. Not everyone can read them, so using them limits the number of people who can read what you wrote, and that generally defeats the purpose of writing something.

The second is that they're inefficient compared to Arabic numerals. Compare a simple number like 1,234. The Roman Numeral equivalent is MCCXXXIV. Look at how many more characters that is than the Arabic numerals, and that's only a thousand. Imagine how many Roman Numerals you'd need to write a number in the billions.

The third is that Arabic numerals are built with math in mind. When you write math in Arabic numerals the equivalent values are in the same places, but with the Roman system they can be all over the place. For example, 9-7 in Roman numerals would be IX - VII. It's very unintuitive to read, and getting from the numbers that you start with to the ones that you'll end up with will mean converting them to different formats.