Why async/await and then produce different results

I’m just asking this question to clarify and get a better understanding at javascript promises. The following two codes look very similar to me, but why both gives different results. Also how to get the result of async/await function in .then way. Thanks.

async/await

const getFieldValue = async (collection, userid) => {
  let response;

  const querySnapshot = await firestore()
    .collection(collection)
    .where("userid", "==", userid)
    .get();
  querySnapshot.forEach((doc) => {
    const { name } = doc.data();
    response = name;
  });

  return response;
};

async function fetchData() {
  const name = await getFieldValue("Users", userid);
  console.log("name", name);
}
fetchData();

.then

const getFieldValue = (collection, userid) => {
  let response;

  firestore()
    .collection(collection)
    .where("userid", "==", userid)
    .get()
    .then((querySnapshot) => {
      querySnapshot.docs.find((doc) => {
        const { name } = doc.data();
        response = name;
      });
    })
    .catch((e) => console.log(e));

  return response;
};

const name = getFieldValue("Users", userid);
console.log("name", name);

async/await returns correct name and .then returns undefined