It's entirely normal. While it's true you can use GSX (with Level 2 too) freely at all FSDT airports, in order for passengers to walk through jetways, they must be SODE jetways, but Zurich used standard jetways that, not being default, are not automatically replaced by GSX.
So, you can consider Zurich to be like any other 3rd party scenery, which requires jetway replacement as explained in this video tutorial here:
http://www.fsdreamteam.com/forum/index.php/topic,18372.0.htmlOf course, in the next weeks or so, we'll release updates for all our older sceneries to support SODE jetways (even for us, with GSX Level 2, it's much easier than before), and we already did it for JFK, but all the others will follow. In the meantime, you can try do it yourself.
Of course, you can still try passengers at Zurich, if you use a parking on the Apron, instead of a Gate.
As of today, the FSDT sceneries that use SODE jetways are:
JFK2 - New York
KLAS - Las Vegas
KIAH - Houston
KMEM - Memphis
KCLT - Charlotte
KSDF - Louisville