This question already has an answer here:
So when I search for best flights from Vancouver to Tehran, I get prices around 1150 CAD for a round trip via Lufthansa which has a stop in either Frankfurt or Munich. Now if I search for the flights from Vancouver to Frankfurt or Munich, the prices don't really change.
That is also true about other Airliners like AirFrance. Surprisingly enough, the cost of a connected flight from Vancouver to Tehran via Air Canada plus Air France which stops in Calgary and then Paris is equal to a single flight from Calgary to Paris!
These are based on my searches on different times of the year, so they're not limited to a specific season.
Why does it happen? Am I missing something?