There’s no requirement for you to upgrade every year if you don’t want to but without it, what would the people who need something new do? I’m upgrading this year from an iPhone X that is really on its last legs. Broken screen, charging more than once a day etc. It’s served it’s purpose well but now is the time for a new one. A two or three year refresh cycle would mean I would be potentially buying a two year old phone today. Why would I want that when I keep things for several years?