I don't think this is the reason. Since Apple stopped making new interesting product lines they are very attentive about not having one line cannibalize the sales of the other(s) as it happened with the iPod and iPhone. This is also the reason why iPads will never run macOS and vice-versa.

Which is simply not true. Decades of touchscreen PCs show this isn't the case. My Surface Laptop 3 is 6 years old with thousands of hours of use (including constant touch and a fair amount of pen) and the screen isn't scratched and doesn't look bad at all.