That's a good question. The British were definitely engaging in a very, very lucrative trade in sea otter pelts from the NW Coast of British Columbia, trading direct to Macau, and the Boston Men/USA got in on that as well over time.

Plausibly some agency (Hudson Bay company?) had a monopoly on beaver trade and this did not apply to sea otter, or maybe the story isn't quite right or there were other economic reasons why beavers to Asia as a concept wasn't exploited.