Either your research is showing that people on average keep their phones longer than 4 years, which seems to line up well with the argument that they don't throw out their phones every 3-4 years for the best new features for no reason;

Or your research is showing that they do churn through at a 4 year rate, which seems to roughly line up with the average battery lifespan and security lifespan across the market. 3 years is right about the time period where I need to replace my phone battery. It would not surprise me at all to see stats that suggest that a lot of people keep their phones until the batteries are unusable or until they're no longer getting updates, and then swap to a new phone -- and across multiple manufacturers, I would not be surprised at all to see that work out to be a ~4 year churn rate, if not a little higher.

I'm not sure what this proves.

Anecdotally, I know more than a few people who prefer Apple devices specifically because of their longevity and support lifespan, so I don't think that the "we have to throw this out because a new phone got announced" characterization is universally true or even necessarily the most common consumer attitude.

I also know people who have bought new phones because the battery was getting weak. I have argued with them to take their phones to a repair shop and to pay $60 to replace the battery, but they felt weird doing that for whatever reason. I suspect some of that might come from the fear of having their phone broken during the repair process before a new one comes in, but that's pure speculation on my part.

And yeah, I also know a few people who have bought new phones just because they care about getting a slightly fancier camera. But I don't necessarily think they're the majority, and an average churn-rate of 4 years across the market would seem to reinforce that point more than anything else.