Maybe because it's not uncommon to test a stolen credit card with some trivial amount first, before making a huge purchase with it. That, combined with it being foreign, probably triggered the fraud alert.
Maybe it's obvious, but if you're having bad experiences with your bank, maybe you should... try a different bank? I can recall only a few instances where my bank has suspected fraud, and they've always called me before my card was deactivated. Once was when I moved halfway across the country, and I spent $350 at Target for random housewares - while I was loading the bags into my car in the Target parking lot, my bank called to make sure it was me. On the other hand, I've travelled to a number of different countries (often without notifying the bank), and I don't recall ever having a problem with my card.
I'll take a stab in the dark, and say it's because my card is through a large but local credit union, where they actually care about individual customers. I think the huge national outfits tend to care about customers in aggregate - if they can offer a better deal than everybody else (e.g. more cash back, or a "double" rewards card), then it doesn't matter if they lose you as a customer - they'll pick up two more to replace you. But that means that to maintain their margins, they have to catch fraud with a much higher false positive rate, because they can't afford any loss.