If you think that all that has changed in the last few years on phones is the camera tech then you should see how well you get on trying to use a modern operating system with the latest apps that are available on an iPhone 7 and see how far you get.
Phones are basically laptop computers in miniaturised form. The more complex programs that become available the faster the hardware needs to be.
Here's a just a few examples of what has actually changed.
Batteries - far more efficient and can last as long as older phones while powering much higher spec graphics cards and CPU's.
Screens - much brighter and higher resolution
Graphics - you can run much more complex 3D applications now
CPU - the apps of today are capable of doing much more than in the past and run significantly faster
Cameras - you have noticed this one because it's something obvious, but without the other upgrades a better quality camera would be laggy and slow and take a long time to process and save the picture once you press the button to take a picture
Wifi - the phones of today have much better WIFI capabilities
Bluetooth - modern phones support the latest Bluetooth which is faster, works over longer distance and has less dropouts
Data - phones now support 5G data instead of 4G