vfrpilotpb,
Trying hard not to bite your head off but I do suggest you read through the archive posts which have been running on this for many months. There has been some excellent debate on this subject by some very experienced pilots and for strictly VFR pilots like me it has been extremely informative.
The simple answer to your question, just in case you are not up to wading through all the posts,is that the Chinook Mk2 was not cleared to fly into icing conditions. The forecast icing level on that day was only about 5 - 600' above the highest ground. To have flown direct it would have had to fly into icing conditions. Another reason, in my view, why this "passenger" flight should never have been authorised under such conditions, and in this aircraft. Again, in my view, this was the responsibility of the senior officers involved and may be another reason why they maintain their stance on gross negligence.