Why won't apple improve their iPhones?

It's like all they do for each new model is put a total of $100 into development of new tech. It's a joke

Because even if they only make a few minor changes with each new version, people buy them and apple makes a lot of money. People still feel the need to have the latest and greatest even if there's not much difference. And if they changed too much at one time they would run out of ideas after they reached their goal

Uh, not really. Apple does a good bit of work towards their iPhones & usually have a feature that is the 1st in the market which subsequent phones emulate. Like the 4 was the 1st to focus on the screen resolution, then the 4S was the 1st to feature a virtual assistant as 2 examples.
Also comparing the iPhone 4S, then the Galaxy S III & then the iPhone 5 it was clear by the performance benchmarks for all 3 that Apple did more than "put a total of $100" into the phone.