When Apple introduced the 12" MacBook, they had all intentions of killing the 11" and 13" Macbook Air (Mid 2015) within 6-9 months, but between the keyboard, the single USB-C port and the price, they underestimated how people would respond to it, which is to say, they did not respect the legacy that the MacBook Air had created. People for months had been asking for Apple to upgrade the screen (50/50 Retina to "at least" IP-S), but Apple decided that they knew better and were going to thrill us with this tiny MacBook.
Here we are 3 years later and the MacBook Air just keeps on selling. Currently, Apple does not have a CPU to put in a new 13" MacBook quite yet, because they know they need to put the latest and greatest for this launch and Intel has not released Whiskey Lake CPUs yet. Or they have not released a 4-core U-Series CPU yet with Iris Plus Graphics.
Apple does not release computers the way PC manufacturers do, and probably never will, although they may make an exception for this launch.