The software also used to be supported for only that long. Support cycles have been getting longer, but so has the price. Batteries also die in a few years.

There are many people who use 5 year old or older iPhones. My dad uses an iPhone 12 (2020), my mum an iPhone 11 (2019), someone else in my family still uses an XS (2018). In one of these cases a dying battery was replaced (which is still much cheaper than a new phone). They all still work very well and fast.

Also a lot of folks around still sporting Samsun S20 (though they should probably ditch them now due to the lack of security updates).

Getting only 2-3 years of life is very bad for most people.