why are we retuning a anonymous function in the below from JS [duplicate]

// Debouncing in Javascript
let counter = 0;
const getData = () => {
  // calls an API and gets Data
  console.log("Fetching Data ..", counter++);
}

const debounce = function(fn, d) {
  let timer;
  return function() {
    let context = this,
      args = arguments;
    clearTimeout(timer);
    timer = setTimeout(() => {
      getData.apply(context, arguments);
    }, d);
  }
}

const betterFunction = debounce(getData, 300);

<input type="text" onkeyup="betterFunction()" />