Question about solidity arrays

Question

Question on the following function:

function getEvens() pure external returns(uint[]) {
  uint[] memory evens = new uint[](5);
  // Keep track of the index in the new array:
  uint counter = 0;
  // Iterate 1 through 10 with a for loop:
  for (uint i = 1; i <= 10; i++) {
    // If `i` is even...
    if (i % 2 == 0) {
      // Add it to our array
      evens[counter] = i;
      // Increment counter to the next empty index in `evens`:
      counter++;
    }
  }
  return evens;
}

What is the point of keeping track of the index of the array instead of simply calling evens.push(i)

Answer 1

because push isn't available for memory and fixed length arrays. as you know memory arrays are less expensive to use than storage arrays.