Other embedded programmers are just that, programmers who found a programming job that happens to be in this sector and learned the peculiriaties on-job.

Also bear in mind that there are different levels of "embedded" which ranges from writing code for some obscure MCU directly in hexeditor (as it is so obscure so nobody bothered to write assembler for it) to writing applications in Java for something that is essentially android tablet bolted onto some larger system (be it car, airplane or some industrial machinery)

Edit: also habing custom hardware is not that capital intensive unless you plan to mass manufacture said custom hardware. And almost any piece of custom hardware has some MCU programmed in C and/or device driver which is also written in C.

Over last 10 years I've participated on development of about 5 different pieces of custom hardware for various niche applications. This includes industrial sensors, IoT-ish stuff and somewhat peculiar reliability and security enhanced PC platform.