Comment by ndiddy

I find Zephyr to be a somewhat poor example. It's typically used on MMUless microcontrollers where the application is linked into the same binary as the OS. I'm sure you'll point out that it's not strictly necessary to use it in that manner, but that's how most people use it and that's how they expect it to work. Licensing it as GPL would mean that basically nobody would use it because it would require releasing your entire firmware source code, especially when there's other permissively licensed alternatives in that space like RTEMS, ThreadX, and FreeRTOS.