It's more expressive than mesh-and-texture, which is the default: it can represent things with poorly defined edges or transparency. Also, because it's solved via GD, you tend to get better fidelity than traditional photogrammetry that relies on MV correspondence.

But also you're just throwing a ton of primitives at the problem; high quality scenes typically have millions of splats. That's a lot of data, so it's no wonder it can be pretty photorealistic. (Still impressive, though.)