Never saw an increase in battery use when using a Samsung device with AOD in use, if they can do it, then Apple can too.
It's never about "can they do it?... of course they can. They've likely built hundreds of its variations in their labs. It's about "can we do it to a level that satisfies our standards for new features?", and that answer isn't always obvious.
AOD is inefficient on LCD displays, and definitely causes burin-in on OLED displays. To avoid burn-in, you have to shift the elements around in a very noticeable way. Just lacks the aesthetic elegance that Apple demands from their UX. And doing it only on OLED iPhones takes something away from the consistency of the iOS user experience that they have across all their devices. It's very easy for Samsung to produce devices that look and feel completely different, Apple however values UX consistency extremely highly, much more than a simple feature such as AOD display.
Others can (and do) add a lot of things that are very easy to implement for Apple, but never passes their QA. While Samsung's design culture is to give users the highest number of features, even if they're ineffective, inefficient, half-baked, inelegant and just out-of-place, Apple's design culture is to not include features if they can't make them effective, efficient, elegant and consistent across all their devices. Obviously whichever of these approaches agrees more with your demands of your device will likely determine if you buy products from either of them.