It might make sense to turn over phones every two years if you are a business that maintains lots of phones.

As an individual, I generally keep my phones for at least five years.

Why should I spend $300 per year instead of $150 when the lower cost option works for me?

(I'm typing this on a 2020 iPhone SE; it runs the latest software. Although this year, that's not necessarily a good thing. Liquid Glass, Safari bugs.)