Airport selection by Oasis is clearly following the LCC model -- choose airports which provide incentives to airlines. Particularly for a "prize" international route. I've heard of some airports in the US offering 100% kickback of all costs for an international flight; still there are few takers. I wonder what incentives Oakland offered (if any).

At least Cologne airport does have a rail link, unlike some of the other LCC airports in the middle of nowhere -- so it could be much worse. The proximity to Bonn might help fill up the J seats, and for tourists Cologne is a great place to land ... so a pretty good choice of the available airports. Interesting that they did not choose Berlin, though (and perhaps telling).