Why unicode is the standard way of converting binary to text?

Unicode doesn't convert binary to text. Unicode encodes text into a scheme that computers understand so that they can display or read text that humans understand.

Back in the day (1960's or so) English text was encoded in ASCII (American Standard Code for Information Interchange). Originally ASCII encoded 127 characters, and could transmit over primitive networks using 7 bits. To fully flesh out English ASCII was extended to handle 255 characters, requiring 8 bits.

As other countries got into computing, they wanted to work in their own languages. A new standard, Unicode was created. Unicode 8 (Unicode is usually referred to a UTF), UTF-8 is basically extended ASCII. UTF-16 can encode all the letters of all the languages in all the countries in the world.