If anything the gap is increasing not shrinking. JVM is terrible at memory access patterns due to the design of the language, and designing for memory is increasingly critical for maximum performance on modern systems. All the clever JIT'ing in the world can't save you from the constant pointer chasing, poor cache locality, and poor prefetching.

The gap won't shrink until Java has value types. Which is on the roadmap, yes, but still doesn't exist just yet.

The problem with those benchmarks is if you look at the Java code you'll see it's highly non-idiomatic. Almost no classes or allocations. They almost all exclusively use primitives and raw arrays. Even then it still doesn't match the performance on average of the C (or similar) versions, but if you add the real-world structure you'd find in any substantial project that performance drops off.