Mary, I don't think there is any particular reason except that Norwegian services cost a lot more! Bear in mind of course that the Norwegians are the same companies (CHC and Bristow) flying the same types (Super Puma and S92) and will be struggling with the grounding of the Super Puma fleet just as we will.
Anyway, hopefully it will be determined that the accident was not as a result of an intrinsic failure in the Super Puma that has not surfaced until now (30 years after inception).