The reason for this, I believe, is that there's no native motion vector data for non-car based objects in AC.
Some guy named SnowyMoon attempted to add a DLSS mod via ReShade a year or two ago - and while it did work, it only worked on the cars themselves. The track, background elements, trees, lighting and textures all went untouched by DLSS. So it was basically a waste of time (and SnowyMoon added DRM to the DLL - which he is apparently notorious for).
It is much harder to do, it seems, than to just slap it into the already-lackluster TAA implementation in AC. In engines like Unreal (blech), everything is motion-vector based from the off - so DLSS/DLAA/XeSS/FSR is a simple plugin to replace the (sh**ty) TAA/TAAU. Not the case with AC. It'd require a major overhaul of the graphics backend, I believe.
TL;DR don't expect it short term - especially since Ilja is much more inclined to pursue whimsy and fancy. He started rain, so much so that the visual implementation is excellent - but just dropped the physics halfway through, so much so that the track goes from "basically the same grip as dry" to "undriveable" in an instant.
He loves this Rally stuff, and has plans to continue it. He (finally) started attempting to alter/improve AI behavior, perhaps the sim's biggest need, with his last preview - but has seemingly abandoned it again on this one.
It's a blindfolded monkey throwing darts when it comes to CSP improvements, unfortunately. Only 71 more patches to go before 1.0! (I kid).
And of course, wait a few days to make sure the bugs don't eat your AC install alive.