I don't buy the patent argument. AV1 is not unique, it would not be hard to find some similarities in the math and argue infringement of one of tens of thousands of patents these companies sit on. The companies simply don't want to upset the largest tech companies, though apple already buys from them.
The AOM foundation has spent millions on legal reviews. There is always a chance of something slipping through, but that could happpen with any technology. Someone unknown company could come forward with a claim that h.265 infringes on a patent.
