https://news.ycombinator.com/item?id=20292762
1. MacOS and iPad are similar, but distinct user experiences. Its more than hardware (one with keyboard, one without), its about those differences in experience. Apple is nothing if not patient about introducing change to computing paradigms and experiences, so it's fine to co-exist for a while. Switching to ARM gives them better margins, better control over price, better control over physical chassis constraints, better control over features offered, access to a better chip team than Intel's, and now TSMC and/or Samsung's better EUV processes. E.g. features-wise, Intel still isn't shipping LPDDR4 chips, something the 4 year old iPhone 6S had.
2. Basically, x86 becomes a co-processor, just like how discrete GPUs are handled. This avoids having to compete with tiny sliver of market that wants Xeons.
3. AMD is a lateral move, with exactly the same lack of control over core technologies problem. Also AMD is historically not as reliable a supplier for volumes that Apple has.
4. See #2 and my comment. Also, they needed to intro Mac Pro to satisfy / shore up existing Mac contingent before they abandoned entirely. This is a multi-year journey.