The virtual machine has been open source for longer. So more academics have looked at, run experiments, written papers... that are then read by the core Java team and sometimes implemented. C# is a bit behind, but should catch-up one day.

That's what it is indeed, more R&D went into Java

C# will catch up eventually, specially now that they invest massively on PGO/AOT and ways to minimize heap allocations (stackallock and struct reference for example)