I held on to my 13 Pro until the 17 pro came out, so I wouldnt be surprised if a lot of this is people finally going "ok maybe now" and the 16 just lands on the biggest group.
I found myself using both phones as I transitioned off the old one and barely noticing the difference mind you, which is a good sign in my eyes. I think Smartphones for the last 6 to 8 years are finally very stable. More stable than a Windows 11 laptop on Hardware people in the 2000s could only dream of.
Besides Touch ID I'd be really hard pressed to tell you something my current iPhone can do that the iPhone 8+ couldn't, let alone something it can do that I use.
2025 and 2024 look identical for the top five spots, just with each number +1, so it's not any sort of one-off thing.
I recently upgraded from an iPhone 12 to an iPhone 16 because I couldn't figure out how to free enough storage on the 12. The battery was still more than good enough to go a full day.
I don't notice any difference other than now I have a pile of useless lightning cables (good riddance). Honestly kind of a relief as I liked the 12 just fine. Phones kind of seem like a Solved tech these days. About as exciting to upgrade them as upgrading my Brother Laser Printer.