It turns out that Tit for Tat remains a very robust strategy, despite its apparent lack of sophistication, in prisoner-dilemma trials.

It's a very robust strategy because of its apparent lack of sophistication. By being easy to detect and predict, it causes its opponents to chose cooperation. Since you do better in PD if your opponent cooperates, a behavior that elicits cooperation is more effective than one that doesn't.

You might say It's effective at being affective.