C# .NET Core 3.1 - Tasks in Ubuntu VM only using 1 vcpu not all vcpus

Question

I have an application that spins up a bunch of HttpListener GetContextAsync' tasks- one per request ideally

However when running a stress test (Hitting it with JMeter) i seem to be CPU bound but to only 50% cpu usage in total (Machine has 2 vcpus)

Is there something i'm missing here or a quirk in .NET Core on linux that is required to get it to run with more than 1 core? It hits and sits at 50% exactly - I've also tried using a Semaphore to limit concurrent connections etc, but no luck

The code that is creating the tasks is below - from my understanding of .NET Tasks they will spin up new threads when required (But will share if not needed) until the thread pool is maxed out - which should result in 100% cpu utilization

        while (_listener.IsListening)
        {
            HttpListenerContext c = await _listener.GetContextAsync();
            Task unawaited = RunContext(c);
        }