Why didn't my snowboard bag make it on the flight at O'Hare despite me arriving over 2 hours early to the airport?

I boarded at ORD (Chicago O'Hare) for a flight to Berlin Tegel via Zurich. I had 2 normal luggage items and one oversized item (snowboard equipment), which I checked in 2+ hours before departure. I was told to take my snowboard bag to the oversized luggage check station, where I left it. I was following with my eyes for about a minute and saw that the guys working the scanners did not move my bag, it kept just lying on the floor. One more guy even asked the other worker if he should put it through scanner, but the other one said no.

With that we left and went through security, then boarded the plane. Upon arrival to Berlin we were told the snowboard bag did not arrive to Berlin. After tedious hours spent at the lost and found counter and then waiting for a few hours, the bag was located by automatic tracing system - in O'Hare! I have a question:

• Given that all the tags were correct, how could it happen that the bag didn't make the flight? Does it have to do with TSA check or potential manual opening?
• What rights do I have in this case? Can I file a compensation claim against the airport?
• Why didn't the airline (Swiss) "notice" that our bag was not on the flight? I have overheard the gate agent saying to another one that the only bag missing was from a transfer passenger (i.e. it could not have been me).