If they didn't have to accommodate people without any RT capable hardware the game could be fully path traced with better performance than currently with RT enabled - albeit would be some specular noise issues which would need probably 2-3x faster hardware again to accommodate the ray budget to eliminate to an ideal level.
What RTX does is instead of simulating every single light ray in a scene, which can sometimes end up giving you say, 20 hours-per-frame instead of 60 frames-per-second, RTX simulates only about 4 light rays per pixel, and then uses some clever hardware to make really good guesses about what the scene would look like if you were to continue calculating the light in the scene to try to give the most realistic scene possible. Nvidia's RTX cards are specially built to make these guesses, which make the scene look much more realistic, but not quite as good as Pixar or Illumination's animation softwares.
Pathtracing. It's the holy grail of computer graphics, it features mind-bending math, needs ridiculous computers to render it, and... looks almost indistinguishable from real life.
With pathtracing, instead of just simulating 5 or 6 light rays to get reflections and shadows and whatnot, you simulate thousands, or even millions, per pixel. Pathtracing simulates what would happen if you took the solid geometry of a scene and put it into the real world with a camera by trying to simulate every light ray that would hit the camera in a scene. Pathtracing looks at all the objects in the scene, and it uses even more math to figure out how light rays will reflect off an object. For example a mirror might reflect the light straight off, but a white wall will reflect in all different directions. The simulation of all the light rays in a scene is called "global illumination."
https://linustechtips.com/topic/1061006-pathtracing-vs-raytracing-disambiguation/
Pathtracing is more an offline rendering method. Also you can just use shaders for pathtracing...
Quake rtx is not a good example of pathtracing. Same with minecraft.
There is only a limited amount of rays that can be cast by affordable graphics hardware.
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