Apple very much did want to invest into AI development, but the financial department - which used to be Cook's department before he became CEO - repeatedly denied allocating money for buying GPUs, and told the engineers to 'just use the old ones'.
At that point, the 'old ones' were several years old, and in quantity about 1% of what Microsoft or Google had at the time.
Apple never 'chose' to wait with AI. It chose to be run by businessmen, who are always clueless, and who will always make terrible decisions. Though in this case it happened to have temporarily positive or neutral consequences for the users.