Because that's not how variables work in JavaScript/Python etc (though it may be fine for say C++ in the case of value types and copy constructors). For example:

I'm typing on phone so for a quick example:

    let a = [];
    let b = a;
    a.push(1);

and consider the value of b now (or the fact that we could write "const" above because the binding is constant, even though we mutate the value). Or see the equivalent for Python by Ned Batchelder, which has more examples and elaboration: https://nedbatchelder.com/text/names1.html