Why is the graviton important when (to my knowledge) gravity isn't a force and thus doesn't need a mediating quantum particle?

Summary

It seems to me that General Relativity is accepted at this point, even in the case of Quantum Mechanics, and my understanding is that GR establishes that gravity isn't a force but just an observed effect of curved space-time. Why, then, is a gravity boson necessary at all? If we have a mediating particle for the 3 fundamental forces that are actually forces, doesn't it make sense that the reason we haven't found the graviton is because it doesn't exist because there's no force for it to mediate?