Loop an array saves only the last value?

Question

I have this code here and i need array of arrays of objects like this

  var cars = [{ a: 1 }, { a: 2 }];
  var arr = [
    { a: 0, name: "as" },
    { a: 0, name: "aa" },
  ];
  var fin = [];

  for (let i in cars) {
    const asd = cars[i].a;
    for (let j in arr) {
      if (arr[j].name == "as") {
        arr[j].a = asd;
      }
    }
    fin.push(arr);
    
    
  }

  console.log(fin);

//output is [[{ a: 2, name: "as" },{ a: 0, name: "aa" }],[{ a: 2, name: "as" },{ a: 0, name: "aa" }]] // put i want it to be [[{ a: 1, name: "as" },{ a: 0, name: "aa" }],[{ a: 2, name: "as" },{ a: 0, name: "aa" }]]

// why does not save fin[0][0] as 1 and it change to 2 then?

//output is [[{ a: 2, name: "as" },{ a: 0, name: "aa" }],[{ a: 2, name: "as" },{ a: 0, name: "aa" }]] // put i want it to be [[{ a: 1, name: "as" },{ a: 0, name: "aa" }],[{ a: 2, name: "as" },{ a: 0, name: "aa" }]]

why does not save fin[0][0] as 1 and it change to 2 then?