The consensus is based on the observation that the propositional sense of “gratitude” is more or less identical to another concept: the concept called appreciation or gladness.

To say that I am grateful that it did not rain on my wedding day, for instance, is just to say that I am glad it did not. To say that I am grateful that my cancer went into remission is just to say I am glad that it did and that I appreciate the extra life and health that state of affairs entails.

By contrast, to say I am grateful to a good Samaritan for saving my life implies more than that I am glad, or appreciate the fact, that I was saved by her.

To be grateful to such a person seems to imply, for instance, a desire to see her fare well, or a commitment to helping her out in the future, should she ever find herself in dire circumstances.