It seems to be highly localized.
If you look at the map in this article, you'll note that the places these feet have been found are along an inner waterway (the Strait of Georgia), not floating in off the Pacific shore. This includes the new find on Westham Island, which is not marked on that particular map, but is on the same waterway. I've added an additional map below. What is misleadingly labeled as "Pacific Ocean" is also the Strait of Georgia.
Something happened in that waterway or near it--maybe a boating accident, plane crash, or some dirty work. Eventually they'll figure it out.