Some reasons why we don't have a super far render distance, in order of importance:

The biggest is GPU memory. The octree that holds the world gets gigantic at large sizes. We'd have to swap parts out as the camera moves. We can do that but haven't gotten there.

Noise: raytracing looks incredibly noisy if you simply cast rays far into small geometry. Hence we even have LOD for blocks, even though they're not needed for efficiency, they're needed for visual stability.

If you're unlucky and a ray has a lot of near misses with geometry, it does more work than other rays and it causes GPU performance degradation. It's rare but to raytrace far you have to optimize for a certain amount of ray steps, we actually put a bound on this.

We find having fog gives some visual unity and sense of scale. With far away fog, the world looks VERY busy visually.