New iPhones are announced yearly, but the average smartphone consumer keeps their device for between 2 and 3 years.[0] iPhones in particular have extended lifecycles; an informal 9to5 Mac poll in 2021 (biased towards enthusiasts) had roughly 4 in 5 people waiting at least 2 years, with almost half of polled users 3 years or more.[1]

So what's actually happening is that the yearly iPhone rush is only a small fraction of the install base upgrading. Sure, there are a few uber enthusiasts that may upgrade every year, but those are a minority, and it's not like those phones go direct to landfills - they're resold. And since there are more opportunities to upgrade, fewer are attempting to upgrade simultaneously, straining supply chains and making Apple's income fluctuate more heavily.

[0]: https://www.statista.com/statistics/619788/average-smartphon... [1]: https://9to5mac.com/2021/04/18/poll-how-often-do-you-upgrade...