About promises and await/async : All examples I find online show that we need to create a "promise maker function" and then call it with await

About promises and await/async : All examples I find online show that we need to create a "promise maker function" and then call it with await
 

promise13 = () => {

  return new Promise((resolve, reject) => { reject(13)})

}



(async () => {

  let num = await promise13();

  console.log('num', num);

})();

what is inherently wrong with this?:

(async () => {

  let num = await new Promise((resolve, reject) => { reject(13)});

  console.log('num', num);

})();