> I always wonder exactly what kind of "systems" these people are programming, clearly not any with real-time constraints.
Well Niklaus Wirth for one was able to design an entire OS using a language (Oberon) that had garbage collection.
> There are a few HFT firms, most notably Virtu, that use Java.
The hedge fund where I worked used Java. We didn't have problems with latency, although admittedly we weren't doing the really low-latency stuff. There are patterns that you can use in Java that basically emulate manual memory management. In Java this is a little harder than in C# because there no value types, but java.nio basically lets you do whatever you want, so you can always allocate everything up-front. In fact, just for fun I did this myself in an audio setting. So basically I had an audio engine with a ring buffer to pass messages to the event loop, and with a little care I was able to ensure that there literally no garbage that made it past the first phase (i.e. locals). Those are essentially free, so basically the GC wasn't getting any pressure at all. It wasn't that hard to write, and with the excellent profiling tools available on the JVM it's easy to see which if you're making use of longer-term GC sweeps or not.
Finally, I would add that there are scenarios where C++ moves into automatic memory management. std::shared_ptr is an example of (shitty) automatic memory management, but there have been efforts, notably by Herb Sutter, to provide precise GC-collection as a library. For some non-blocking multithreaded algorithms, GC schemes are actually necessary since allocation becomes one of the prime vectors through which blocking occurs.
So conclusion, while it's certainly the case that most systems programming is done in languages with manual memory management, it's a little less binary than you suggest. That said: I'm writing a DAW (zenaud.io) and for that I am using C++, mainly for memory management :)