Flying to Tallinn

We have to Fly America, and that's OK with me. It's a bit tricky though. If you use Expedia for example, you can get from St. Louis to Tallinn for ~$1,000, or maybe to Helsinki for $800 (the ferry is about $60 round trip). But that's on SAS or Lufthansa and I need an American flagged carrier. American, Delta, United all list fares of about $2,000 to Tallinn, or higher. Continental says $900 to Helsinki or Stockholm, but you can't get a fare all the way to Tallinn. SO, I bought 4 round trip tickets to Stockholm on Continental for $900 each. It's only $200 each for round trip airfare to Tallinn from Stockholm. So for the minor inconvenience of picking up our baggage and checking right back in on another airline, we save about $900 each. Since we go through customs in Stockholm anyway, it's not a big deal. Why is it so difficult to work out travel?