Phi-Bi

Most tropes aren't necessarily invented, more like "discovered", though not in the way we think of it. When something gains enough traction or notoriety, then it sometimes rises into the level of tropes. Rei Ayanami expies for example. I'm pretty sure it would be very difficult to create a new trope, because the surge of mass media makes it so that many people have already explored nearly all forms of it, thus making sure that tropes are somehow "discovered"/invented.