Why does eventListeners only execute if radio is physical checked?

Question

Problem

I'm not understanding why the input addEventListener change only execute when I physically check the radio input.

The event should fire every time the radio button is checked.
But it refuses to acknowledge if javascript checkes it (whether by click or onkeydown)

How would I get javascript to fire addEventListener change regardless of how it was checked?

Demo

To console log:

• Press 1 or 2 (javascript does not acknowledge radio being checked)
• Click the sentence (javascript does not acknowledge radio being checked)
• Click the radio button

let input1 = document.getElementById("input1")
let input2 = document.getElementById("input2")
let div = document.getElementById("div")



//Listens for keypress and checkes one of the radios
document.onkeydown = function (e) {
 if (e.key==="1") {input1.checked = true;}
  if (e.key==="2") {input2.checked = true;}
}



//Listens for sentence click and checkes one of the radios
div.addEventListener ("click", function () {
  if (input1.checked){input2.checked = true;}
  else {input1.checked = true;}
})



//When ever inputs are checked
input1.addEventListener ("change", function () {
 console.log("Radio1 was checked")
})
input2.addEventListener ("change", function () {
 console.log("Radio2 was checked")
})

#div {
  padding: 10px;
  background: #f5f5f5;
  border-radius: 5px;
  margin: 10px 0;
  user-select: none;
}

<div id="div">
Click radio, click this sentence or (Press 1 or 2) to log
</div>
<input type="radio" name="a" id="input1"/>
<input type="radio" name="a" id="input2"/>