"it usually lacks many facilities commonly found in desktops or servers." This is where they implied that operating system level functionalities are not found

"it usually lacks many facilities commonly found in desktops or servers." This is where they implied that operating system level functionalities are not found on computers without operating systems. The fragmentation that exists in embedded is due to the nature of embedded systems, not programming languages. PCs, laptops, and smartphones are general purpose computers. Just about everything else is an embedded device, hardware custom designed for a specific purpose, given just enough resources to accomplish its intended task. Writing software for a general purpose computer on top of a full OS can largely be done without caring about the underlying hardware. Writing embedded firmware without an OS is only possible through understanding the specific hardware you are targeting.