There was a video by PolyMatter recently on the economics of why Apple cannot yet move the bulk of iPhone manufacturing away from China (available on Nebula and on YouTube). This is perhaps the singular quote which helps answer your question, around the 02:35 mark:

Any country can assemble the iPhone. But Apple doesn't need to make an iPhone, it needs to make 590 every minute, it needs 35,000 per hour, 849,000 per day, 5.9 million per week. That's the challenge facing Apple.

The sheer scale of Apple's manufacturing -- setting aside Samsung's also humongous scale -- means that there might not be a supplier for that quantity of large image sensor or new-tech batteries. Now, Apple could drive that sort of market, and they probably are working on it. But as the video explains, Apple's style is more about finding an edge which they can exclusively hone, up to and including the outright buying out of the supplier. This keeps them ahead of the competition, at least for long enough until it doesn't matter anymore.

In some ways, this might sound like Apple has a touch of Not Invented Here Syndrome, but realistically, consumers expect that Apple is going to do something so outlandish and non-standard that to simply be jumping onto a bandwagon of "already researched" technology would be considered a failure. They are, after all, a market leader, irrespective of what one might think about the product itself.

Historical example of heavy R&D paying dividends until it stopped being relevant: Sony's Trinitron CRT patent expired just around the time that LCDs started showing up in the consumer space. Any competitor could finally start producing CRT TVs with the same qualities as a Sony Trinitron TV, but why would they? The world had moved on, and so had Sony.

In brief, Apple probably can't deliver to the world a new iPhone with massive image sensors right now. But that certainly doesn't mean they wouldn't have their camera team looking into it and working with partners to scale up the manufacturing, such as by increasing yield or being very clever, probably both. Ever since that one time an iPhone prototype was found in a Bay Area bar, their opsec for new prototypes has been top notch. So we'll only know when we know.

The latest tech isn’t proven to last, might be harder to integrate, might require making design choices that affect the production line, the reliability of the phone, the battery longevity, the supply chain, the operating system, etc. Using the newest tech is a surefire way to make sure you have to do a recall, if you’re the biggest companies on the planet.

Most people don't really care about cool tech, they want a phone that just works

Ask any apple fanboy/fanatic and they will tell you, and they will be correct: Apple rarely leads the charge. They wait and they bide their time, and they watch how a technology is applied and how it works well and how it fails, and then they engineer a solution that they believe to be a smoother user experience to everyone else, and only then do they drop a new tech.

Budget phone makers are trying to stand out and captivate a much smaller market segment, so they have to go big or go home, or else no one will care.

The big guys are so big that they can actually use the market itself as market research, and the big guys are so big they can hold out until they know they have a stable, proven solution.

A marketing prof once told me that a lot of phone companies, Apple in specific, split their projects up into several releases as a form of planned obsolescence. You're more likely to find this in matured and established brand names because they have the power of goodwill to retain their market share whereas an up and coming company relies on being innovative in the sense of being early adopters of new, sometimes not fully tested, technology.

So for example, you see 3 iPhones being released in the span of 2 years. Those were likely 1 project released in a deliberately staggered manner so that "fanboys" "early movers" "brand loyal" (basically materialistic people who either don't understand or love being manipulated by corps) will pay for 1 project that a team worked on, 3 separate times.

Samsung, being the largest manufacturer of South Korea, has an incentive to keep their production as in-house as possible. Which is why they're reluctant to license technology that they can build themselves, such as cameras.

SiC batteries would also help a lot for thinner phones like foldables (see Find N5 and XFold 5 from Oppo and Vivo compared to Samsung’s Z Fold 7) as well “thin phones” (see Samsung’s S25 Edge and Apple’s rumoured 17 Air)

Another thing, Qi2! Only Apple and the HMD Skyline support it. Why is that?