Q: Why do most of these ancient 'Dowlings' not have a Dowling surname?
They are mostly all older than the invention of surnames.
Surnames, or family names, are a relatively a recent development and common use of a surname only really started in the 15th century. HOWEVER, in Ireland, the use of surnames has an even older history. Ireland was the first country in Europe to use fixed surnames. As noted in the Annals, the first recorded fixed surname was Ó Cleirigh, which recorded the death of Tigherneach Ua Cleirigh, Lord of Aidhne in Galway in the year 916. Of course, consistent spelling came much later!