There's a variety of possibilities. Lerc mentions GC as one possibility, which could definitely be the case. Another one that would be high on my "first guess" list is that everything above it has much better optimizers, and raytracing code is one of the places this is really going to show. Go does basically very little optimization, because it prioritizes fast compilation.

(Where Go "wants" to play is that same benchmark, except including compilation time.)

A couple of the things below Go I suspect are bad implementations. I would expect a warmed-up C# to beat Go if both have reasonable (not super-crazy optimized implementations) or at least be at parity, and Luajit may also be a slow implementation. In both cases because ray-traced code is a great place for a JIT to come out and play. EDIT: Oh, I see C# is Mono, and not the Windows implementation. In that case that makes sense.

Oh, and I find it helpful to look at these things logarithmically. I think it matches real-world experiences somewhat better, even though we truly pay for performance in the linear world. From that perspective, it's still only the second largest. The largest is Haskell to Elixir, which is substantially larger. O'Caml->Go is large, but not crazily so; several other differences come close.