Isn’t this because they have to pay Red for their ridiculous patent of compressed raw video?

CinemaDNG is not always compressed. I have a BlackMagic camera that records uncompressed CinemaDNG. Also, DJI has gotten around some of this by putting the recorder in the body of the drone, making it technically not part of the camera.

However, the oft-repeated claim that Red's patent applies only to internal raw recording does not hold up when you consider that Apple and Atomos have to pay extortion for ProRes Raw, which is used in EXTERNAL recorders.

It's also only available bundled with ProRes, although it's almost certain there's also some backroom RED RAW-racket deal going on too.

Well, that's DJI's decision.