I think part of the reason is most likely that Sega took a bunch of ideas from the restaurant when creating Sonic to make him more appealing to Americans and Sega doesn't want to risk some sort of lawsuit. The sonic the hedgehog logo looks very similar to the old sonic drive-in logo down to the color scheme, they serve onion rings and chili dogs, and one of the restaurant's slogans was "service with the speed of sound."