I think some people just enjoyed the days when a new iPhone year could be a more dramatic difference. But iPhones are far more mature, and the software is built to support a large number of phones. It's not realistic to expect huge changes every single year anymore.
I stopped expecting huge changes after they released the iPhone 6S....to me, getting that phone was the moment I didn't feel very restricted in my day-to-day use on a phone. It was great for browsing the web, using media content, had 2GB of RAM and a great processor which kept things fast without as much reloading.
That's why I used that iPhone 6S until today, 5 years later. I simply did not see the reason to upgrade. In reality, the iPhone 12 is going to be one of the bigger updates in recent memory. A redesigned chassis, improved ceramic shield, standard OLED displays, and 5G capable which may not be important now but could be important in a few years.
My iPhone 12 Pro is a great improvement over my 5 year old iPhone 6S. To me it's almost perfect for what I want out of a phone. The improved Chassis design harkens back to the iPhone 5 which was my favorite phone form factor of all time and just looked premium. Everything works flawlessly on the new iPhone 12 and I am definitely appreciating the extra screen real estate and snappy apps.
However, I will not be looking to upgrade for a long time either, just like my iPhone 6S. This phone has 5G, it has 6GB of RAM, it has an incredibly fast processor. So unless AT&T introduces a similar promotion and I can trade in my 12 Pro for a free upgrade after my 30 months is up, then I very likely could hold onto it for 6-8 years. The reality is that there's nothing much on the horizon now that's a game changer.