So do raytraced reflections - in any game, not just racing.
Also I actually call BS on that - most games I had inside view of, just used the standard scene render with reduced draw distance (for obvious reasons), and LOD would only adjust in so far as resolution of reflection was lower. It's far more common to do optimizations like reduced update-rate of some (or all) cube faces. But hey - RT does that in some games too.
play Need for Speed Unbound, drive next to a parked car, look at that car in your car's reflection.
turns all of them into cybertrucks lol.
Cars are not rendered for the same reason self-reflections are problematic - you end up in a recursion where things reflected just look plain wrong. If you can avoid that (some games do) you can happily render car-reflecting each other with cube-maps (some games do).
And the number of probes is entirely arbitrary - I've seen everything from 1 for everything in the scene (even static objects), to spatially distributed probes (so sharing is distance dependant), to 1 per dynamic object. Especially if you do all the associated optimizations you said were 'standard', and you aren't running an engine that is crippled by more than 1 camera (which to be fair - some middleware do suck at), a probe adds so little to the render time you can have dozens of them without a problem.
they look fine in cubemaps in almost any scenario. the aforementioned Need of Speed Unbound includes parked cars in their cubemap (which is rendered once for your car and is applied to all cars, never seen it done differently tbh)
it works, looks fine from a distance too, but it is costly so only parked cars are included. and I think they get removed the moment you hit (and therefore move) them.
the same is true for trees and barriers that can be knocked down.
RT being 'CPU intensive' is mostly a false narrative outside of certain specific platform constraints (that aren't console specific). More importantly - for raytracing a car reflection - all we need is a BVH of environment that can be precomputed once (no runtime overhead to update) and a number of cars with their own BVH each (again - virtually no runtime overhead to update for GT where cars aren't destructible). The rest is smaller dynamic objects which - well in case of GT are next to nothing.
The case for 'BVH update comes at a cost' would be open-world like Forza Horizon - but that could still be mostly streamed precomputed with modern SSDs.
RT reflections force you to render things outside of your camera. and yes, the cubemap reflections in car games already do that, but at a way lower quality than even Spiderman's super low quality LODs it uses for its RT reflections.
not to mention lower resolution as well typically. which you can not reduce as much when using raytracing, because if you reduce the resolution too much you will cross a line where the reflections will look so noisy that you ruin the visuals to a point that it makes them a visual downgrade over cubemaps.
Forza is actually not far off from hitting this line.
Cubemap reflections can be ridiculously low res and still look ok at a distance.