There are lots of different programming languages in 4 different paradigms:
I could write a program in all programming paradigms e.g a fraction that I could write it using classes in OOP and also I could write it using functions in a functional programming language. So why do we need diferent proglangs and paradigms?
Programming paradigms exists for the benefit of programmers themselves. They all represent different attempts at creating a common platform of abstraction that are as beneficial as possible when starting to solve arbitrary problems. Turing completeness clearly states that any program can basically be written in any programming language that satisfies a certain basic set of rules. Therefore it makes little difference once the program is running what paradigm it is written in. The important part is that there is a person or a group behind it that can maintain or enhance it well (and then again we are back at the persons writing the program).