Pushed into 2019 are a number of features including a refresh of the home screen and in-car user interfaces, improvements to core apps like mail and updates to the picture-taking, photo editing and sharing experiences.
This isn’t a new strategy for Apple—they have used this strategy in macOS for a number of years and it’s worked great. With all of the new features in iOS over the past several years, the time had to come when Apple took a step back and focused on reliability and performance.