Apple was selling more SoC for iPhone than Intel is selling CPU per year. I am not entirely sure where that risk are.

A MBA accountant type would support that move simply on the basis of replacing an expensive external vendor with a more affordable internally sourced chip and increasing profit margin.

The A4 was shipped in 2010. The playbook to use them in laptops might have been discussed before Tim Cook took over. He executed very well nevertheless, though that's what he is known to excel at anyway.

Apple's foray into producing their own chips started under Steve Jobs. They bought PA Semi in like 2008. Devices with the A4 launched in 2010.