The problem with "unlimited detail" wasn't that it was static (the majority of any game's environment are), it's that it was using voxels which can't really compete with triangles when it comes to a quality-perf trade-off. They could render massive data sets, but not with a quality that is needed for games. Voxel-based data sets tend to require a whole lot of memory, whereas triangle-based data sets can cheaply "fake" higher details with textures. The blockiness of voxels is also a huge issue for anything that's not an axis-aligned-bounding-box, and to fix that you have to invest so much GPU resources, you might as well go back to textured triangles.

I wouldn't be surprised if gaussian splats make it into AAA games, though. Not as the main rendering primitive, but for specific things like vegetation where they really kick ass.