Age, possibly. Ternus has 6 more years until retirement than Federighi.

To what extent do you think Apple software has done well under Craig's leadership?

He could have not wanted the job to begin with. CEO is no joke, and for him would mean to say goodbye to software forever.

I wish he would say good bye to software forever. Apple software is getting worse by the minute it seems.

Some design stuff are quite bad like the Liquid Glass, but the rest is fine I think. The M series wouldn't have gone as well as it did if software side wasn't up for the task