My impression from the tech press/tabloids is that apple was somewhat forced to switch away from Intel because Intel had begun to stagnate. Intel was stuck doing 14nm+ iterations and could only ship slow inefficient chips, resulting in very noisy and hot apple laptops.
Maybe apple could have stayed with x86 from AMD with some sort of co-design, but apple likely preferred to design their own chip so they would control the whole process and keep more of the profits. Designing their own chip also seems like it allowed apple to leverage their investments in TSMC for making their phone chips to also include their laptop chips. I wonder whether they already had a long term plan to dump Intel, or whether the plan started as a reaction to the serious problems that began developing at Intel years ago.
Maybe apple could have stayed with x86 from AMD with some sort of co-design, but apple likely preferred to design their own chip so they would control the whole process and keep more of the profits. Designing their own chip also seems like it allowed apple to leverage their investments in TSMC for making their phone chips to also include their laptop chips. I wonder whether they already had a long term plan to dump Intel, or whether the plan started as a reaction to the serious problems that began developing at Intel years ago.