The housing market is really a separate subject to tourism and I agree second homes are a largely unwanted aspect that seriously affects locals, we have exactly the same along stretches of the Northumberland coasts for example.
The tourists that bring in most of the expenditure visit for short spells in vehicles staying in rented cottages, B&Bs, hotels, static and touring caravans and day visitors and spend money in pubs, shops and restaurants. Many of those are from abroad and none of these have the second homes you mention.