Why asynchronous code is so much slower than synchronous code

I create a test table in SQL Server like this:

CREATE TABLE Person
(
    PersonID INT NOT NULL IDENTITY,
    PersonName NCHAR(500) NOT NULL,
    PersonFamily NCHAR(500) NOT NULL,
 
    CONSTRAINT PK_Person PRIMARY KEY(PersonID)
)

Then I create two methods to test async.

The first method uses an async approach to read all person, and the second one uses a sync approach.

Async method:

private async Task<List<Person>> ReadPersonsAsync()
{
    List<Person> result = new List<Person>();

    using (SqlConnection sqlConnection = new SqlConnection(ConnectionString))
    {
        using (SqlCommand sqlCommand = new SqlCommand())
        {
            sqlCommand.CommandText = "SELECT * FROM Person";
            sqlCommand.CommandType = System.Data.CommandType.Text;
            sqlCommand.Connection = sqlConnection;

            await sqlConnection.OpenAsync();

            using (var reader = await sqlCommand.ExecuteReaderAsync())
            {
                while (await reader.ReadAsync())
                {
                    result.Add(new Person
                    {
                        ID = int.Parse(reader[0].ToString()),
                        Name = reader[1].ToString(),
                        Family = reader[2].ToString()
                    });
                }
            }
        }
    }

    return result;
}

Sync method:

private List<Person> ReadPersons()
{
    List<Person> result = new List<Person>();

    using (SqlConnection sqlConnection = new SqlConnection(ConnectionString))
    {
        using (SqlCommand sqlCommand = new SqlCommand())
        {
            sqlCommand.CommandText = "SELECT * FROM Person";
            sqlCommand.CommandType = System.Data.CommandType.Text;
            sqlCommand.Connection = sqlConnection;

            sqlConnection.Open();

            using (var reader = sqlCommand.ExecuteReader())
            {
                while (reader.Read())
                {
                    result.Add(new Person
                    {
                        ID = int.Parse(reader[0].ToString()),
                        Name = reader[1].ToString(),
                        Family = reader[2].ToString()
                    });
                }
            }
        }
    }

    return result;
}

When I use the async approach it takes 10 seconds, but the sync approach is run in 2 seconds.

Which part of my code is wrong? Thanks.