The song wasn't very good in the first place (and it is a song contest, allegedly), and secondly the numbers phoning in to support Dervish because they were a traditional band would always be hugely outnumbered by the pop music fans in any country.
I didn't see the contest myself but having heard the record a few times I thought Dervish did their best with a fairly ropey song, which was by all accounts the best of a bad lot of shortlisted entries. From Dervish's point of view the contest has helped to raise their profile in Europe, and at home.
I was amazed at how few people I was talking to, outside of the folk world here in Ireland, had ever heard of Dervish before they were selected for the contest.