JIT compilers are in general not great at auto-vec because it is an expensive optimization, they do not have as much time as eg C++ ahead-of-time compilers, so the JVM and the CLR only handle very simple cases. .NET has an explicit API to guarantee vectorization, Java does not, but there is a JEP: https://openjdk.java.net/jeps/338

I don’t know about Golang, but given the compiler speed it probably can’t afford the more advanced techniques.