I know correlation doesn't imply causation, but I'm going with it: https://i.imgur.com/fyveqs3.png
edit: chart of AAPL stock price for the past 12 years
edit: chart of AAPL stock price for the past 12 years
What we do know is that iPhones are important to Apple and if they genuinely thought that there was a significant market for tiny phones then they would release one. They still sell the iPad mini and the smaller Apple Watch for example so it's not just they they are afraid of small things.
But still you see a lot of comments even here that Apple would be saved if they released a new iPhone SE or some other small phone.