You're working in harsh weather. You can't see shit. You have these client ships that are very slow and very large and very expensive. If you even *touch* one of the client ships, that's $3m, minimum, instantly.
An icebreaker would go right through an oil tanker, and come out the other side of it with a broken radar antenna, covered in oil.
And the icebreaker runs in front of the client breaking ice so it can get where it's going.