Ironically, I think the accessibility focus started because they were a fraction of today’s size: in the early 2000s, section 508 requirements were becoming more stringent; there was an increasing risk that Apple would get shut out of government contracts, and due to the small market share of OS X, it was not considered a viable market for commercial screen reader vendors, so Apple decided to roll their own.
Thanks to strong leadership in the accessibility team, there was an increasing buy-in from the top, and throughout the company. Today, accessibility is indeed in Apple’s DNA, but initially, there was quite a bit of genetic engineering and (dare I say it?) government regulation involved.
Apple was known for easy to use in the 1980s. While that isn't entirely accessibility, the two are related. The early macs had some accessibility features.
Thanks to strong leadership in the accessibility team, there was an increasing buy-in from the top, and throughout the company. Today, accessibility is indeed in Apple’s DNA, but initially, there was quite a bit of genetic engineering and (dare I say it?) government regulation involved.