Because, on one side, we've been able to deduce, in principle, all such interactions (and there are maaaaany) from just two. So it'd be surprising. On the other

Because, on one side, we've been able to deduce, in principle, all such interactions (and there are maaaaany) from just two. So it'd be surprising. On the other hand, these two interactions, General Relativity and the Standard Model, talk about the exact same things (the same "statements" in your example). While in many energy ranges the effects of one or the other are too small to be noticed, there definitely is an energy range in which both should have strong effects. Yet they aren't compatible. If we performed experiments in those ranges, the theory that describes what we measure would need to be compatible with both, an extension; the unified theory.