Rust is a modern, memory safe systems language. The code you write compiles to native machine which executes in a predictable way every time you run it.
If you need to write firmware for, say, a satellite, C# and Python are out because they have an intermediate step between your deployable and the machine instructions you eventually execute. You have an external dependency which adds a level of unpredictability. All three of your example languages are out because they are garbage collected languages, which makes them inherently unpredictable at runtime. The last thing you want is an OOM in the middle of a rocket engine burn.
Go and C# are competing with Python, Java, Ruby, etc. All languages you would write a web application in, but not a satellite's firmware.
1. You can get an OOM error (or a stack overflow) in most languages (including Rust).
2. Safety-critical hard realtime systems require far more determinism guarantees than a language/runtime alone can provide. For example, they require deterministic scheduling of threads (usually round robin with very strong prioritization guarantees and bounded task-switching latence), and so require a realtime OS. Also, safety-critical realtime systems have ways of guaranteeing bounded memory growth, for both the stack and the heap. These exist in specialized languages for realtime such as SPARK (an Ada variant) and SCADE.
3. Java is actually used in safety-critical hard realtime systems, including avionics, but in a special, hard realtime JVM that has different kinds of deterministic guarantees (when run on a realtime OS), including memory allocation, scheduling and hard deadlines for asynchronous events (see https://www.aicas.com/cms/en/rtsj). What's particularly cool about realtime Java is that it allows for a safe mix of realtime and non-realtime threads, as even in realtime systems, the actual realtime part is usually a small portion of the program.
Someone hasn't payed attention to the AOT compilers available for C# and Java, their widely deployment on embedded platforms, PTC, MicroEJ, Aicas, WebSphere Real Time, Android Things, wearOS, Ricoh, Cisco, Netduino, Meadow, IoT Core and many others.
Yes, maybe not on a satellite's firmware, but on a Gemalto firmware, certainly.
If you need to write firmware for, say, a satellite, C# and Python are out because they have an intermediate step between your deployable and the machine instructions you eventually execute. You have an external dependency which adds a level of unpredictability. All three of your example languages are out because they are garbage collected languages, which makes them inherently unpredictable at runtime. The last thing you want is an OOM in the middle of a rocket engine burn.
Go and C# are competing with Python, Java, Ruby, etc. All languages you would write a web application in, but not a satellite's firmware.
Rust is competing with C and C++.