RYR always find someone else to blame when they need to downsize. I remember this winter when "because of a strike at Boeing, we will not have enough airplanes, so we need to cancel a couple of thousand flights". In the end lots and lots of brandspanking new 738's stood on the ground, only because there were not enough crews to take them flying. All of them on the 900hr limit.
Anyway, a tax that will not cost the airline anything is hardly the reason for removing some lines if they are performing well. But it's a way to keep Nyköpings kommun and other cities in line and let them know that the money better keep on coming or they will be cut out. It's also a way of blaming the swedish government instead of saying that the lines are not good enough since RYR are always expanding and they can do no wrong...