The Acad is obviously correct. There are several, and complex, reasons why traffic doesn't always land were we would like. I reccomend you follow the thread on the forum about the Zurich afcad, so you willl undertand the issues involved, which are common to flight sim.
Also, I'm moving the message under the Zurich area, but it would have helped if you said which version of Zurich, FS9 or FSX, you were referring to.