To my knowledge the FSF doesn't consider firmware blobs with no way to flash "part of certification" because it would be inoractical to do so. By definition "software you can't change" isn't "free"(as in speech, not beer), so I don't think it's an ideological line.

So they either have to consider any device with unmodifiable software to be non-free(basically removing entire device classes), or be realistic and draw the line somewhere. "Can you modify the software on the device from the rest of the gnu software" is a line that matches up with their ideals fairly well IMO.

Basically, Richard Stallman is well aware that cars are bundles of non-free software(see: https://jalopnik.com/richard-stallman-weighs-in-on-the-check...). He has voiced opinions that software controlling the brakes in your car should be FSF and not binary blobs that come pre-installed with no visibility.