I've often wondered why DUB is only served 3 x daily by FR? It is one of the most popular destinations from Luton and has in the past been served on a more frequent basis and could surely sustain 4 or 5 flights per day and must be profitable, so am surprised FR don't make more of the route.
The route used to have more flights but was cut back when their 737-200's were retired as the replacement 737 had more seats.