RTOS are in everything! They make a ton of sense if you have a lot of resources to manage or calls to external services that may block for some time, like a modem connection. Lots of IOT products have RTOS's running under the hood, where running a kernel even as stripped back as Linux can be is too expensive computationally. And with less kernel/OS overhead, a true hard real time system can be implemented with a pretty strong guarantee of safety (not crypto safety, operational safety). There's a reason Amazon bought FreeRTOS a while back.