The VNO-DUB-VNO was never oing to work with both Star1 and BT on the route at almost the same times and days of operation
But what really killed them of was FR's KUN-DUB and KUN-LON. FR has massively increased KUN-UK recently, and STN-LON was Star1's main connection.
Not forgetting that for most of Star1's history
Aer Lingus was also an unwelcome competitor for them with their routes: Dublin to Vilnius and Gatwick to Vilnius.