Question

Why doesn't Gravitons have charge?

Answer 1

A graviton is really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really hard to detect.

Detecting a photon, for example, is extremely easy. There many types of devices that are able to detect single photons, such as photomultipliers, used in labs around the world. In fact, you don't even need any fancy technology; the human eye can, in principle, detect a single photon.