[_ph_]

On the surface, there isn't so much new in Catalina oder iOS 13, that you would think that things break so badly, but they did. Starting a new branch of the development always is a disruption. Developers would be reassigned to new groups, probably the best ones even, new developers would join the existing groups. This process probably has started like 2-3 years ago and intensified like 1-2 years ago, especially after they had the first silicon to play with - and I assume the CPU will be sufficiently different from an iPhone so that you want to at least optimize your code for it, there might also be entirely new features to support.