This is the part they’re missing: apple actually care about the appearance of quality.
I’m not saying apple makes quality products, there’s some good debate there that they really don’t. But they certainly foster the belief that apple products are superior in quality to their competitors.
Unity is a great engine when it’s used well, but it doesn’t have a reputation for quality. It has a Reputation that says “anyone can publish a bolted together asset flip and make a quick buck off of twitter hype”
I doubt apple would acquire unity based purely on the fact that unity does not adhere to apple’s ideals on branding. Apple tends to buy rights from young companies that don’t have large established brands yet, because it’s easier to fold them into the cult of apple. An established brand with a known reputation would be a tough sell, especially when Apple has the resources to simply make their own product that’s tailored to their hardware.