Why does the following code not work ?

```
\Requirepackage{amsthm}
\renewcommand\newtheorem[2]{%
    \NewEnviron{\csname #1\endcsname}[1]{%
        ##1 : \BODY
    }
}

```

I have seen examples of the use of `\csname SOMENAME\endcsname` for macro with no arguments but I do not know how to do it with a `\NewEnviron` or a `\newcommand` having multiple arguments.
I am prompted with the error `! Missing \endcsname inserted`.