That might be a reason. It could also be to do with transatlantic connections or simply availability of aircraft I suppose.
Incidentally, it does seem that easyJet intends to return to the BRS-KEF route next winter after dropping it from next April. The linked report (below) says that winter passenger numbers rose considerably but summer saw almost no growth.
Whether they will have that re-think now that WOW has arrived remains to be seen. If they don't and resume at this winter's schedule 6 x weekly across both airlines seems a lot of seats to fill, even with some transatlantic onward connectivity.
The passenger numbers in the report for January-August are incorrect according to CAA stats with twice the number flying than shown in the report.
easyJet reduces Iceland-Bristol to winter only - Iceland Monitor
Remaining with easyJet, Catania has re-appeared in the booking system for next summer, again at 2 x weekly but commencing slightly later in early June.
Of matters generally at BRS, the CEO hinted in the recent consultative committee minutes that further growth can be anticipated in 2016.