1) aesthetic is more novel than polygons, which are currently much more widespread (note: novel does not necessarily equate to "better" looking).
2) The finite limitations "leave more to the imagination" - in the same way that low resolution pixel art might, vs a high resolution vector image.
3) A very minor factor, but worth noting: not only are voxels visually novel, but they are technologically novel - in order to make a competitive voxel engine, you typically are not using an off-the-shelf engine like Unreal or Unity (though you can, and there are many voxel pluggins for these engines). Thus programmers are drawn to them (IMO) - they are an easy way to visually show off your technical know-how, just as you might many other effects in the demo scene.
4) A false sense of nostalgia - voxel engines never were very widespread, and the closest thing in the early days tended to be height-map driven rather than volumetric (the earliest notable exception being Voxlap). But the "nostalgia" exists, just as it does with synthwave (most of which does not fully mirror any music of the 80s/90s).
5) Voxels are point-based volumetric representation and thus are much easier to use for procedural generation (vs describing a surface, which is much harder). Though voxels are often wrapped on the surface with polygons, this is trivial (vs, say, describing the polygonization of a metaball without using voxels).