Why is a direct flight twice as expensive as a flight with 1 stop where the stop is the same city as the destination of the direct flight?

Question

As the title shows I found the following:

1 direct return flight HK->Vancouver-> HK, priced at HKD 10600

and

1 return flight HK-> Vancouver -> Seattle -> Vancouver -> HK, priced at 5200 HKD

How is that possible? I understand Air Canada might want to compete with different American airlines that are able to service Seattle but I saw the same weird pricing offered by Korean Airlines and other non Canadian/non American airlines.

My question is this: With the 1-stop flight, can I get off in Vancouver and not partake in the 2nd leg of the journey? Can I collect my suitcases at Vancouver even if the final stop is Seattle? Even more important, on the way back to Hong Kong, can I board the flight in Vancouver instead of in Seattle?

I am just wondering because despite all potential reasons of price discrimination, and other marketing techniques that may attempt to explain this price discrepancy, I find no logic in how those 2 different flights are priced at all. Can someone explain?

Thanks

---

Here the flight with 1 stop , 1/2 price, and the first leg being the exact same as the direct flight.

---