Like everyone said, a confluence of factors: Higher demand in the U.S./lower demand in Canada, lack of domestic production, export costs, pricing in U.S. dollars/weak CDN dollar, regulatory costs.
I would not be surprised if costs exploded over the coming years. If the Liberals aren't stupid, they'll make ammunition control just as important as gun control to advance their agenda. "You want to be out of compliance with whatever gun registry/banning we implement? Fine. What are you going to feed that rifle if we control commercial ammunition and reloading components?"
The Messiah in the U.S. knew that when he ordered the ATF to go after M855/Greentips. And don't think that story is over.