Pure economics and an unwillingness to invest in older fabs made the GPU a first class citizen in Intel silicon terms, but Intel management still didnt have the motivation to dedicate more die area to the GPU. That encouragement would come externally, from Apple.
Looking at the past few years of Apple products, youll recognize one common thread: Apple as a company values GPU performance. As a small customer of Intels, Apples GPU desires didnt really matter, but as Apple grew, so did its influence within Intel. With every microprocessor generation, Intel talks to its major customers and uses their input to help shape the designs. Theres no sense in building silicon that no one wants to buy, so Intel engages its customers and rolls their feedback into silicon. Apple eventually got to the point where it was buying enough high-margin Intel silicon to influence Intels roadmap.