at scale, delivering cost-effective infrastructure matters to the bottom line, even for seemingly unrelated cash cows like ads. the larger the infrastructure footprint, the better economies of scale and amortization of R&D. there is a race to deploy the largest infrastructure (datacenters) economically sustainable. as external demand dwarfs internal demand, and as infrastructure is delivered to external customers via Google Cloud, Google Cloud is a long term strategic bet.
side note: the datacenter build out race is an early instance of the paperclip optimizer phenomena, with datacenters instead of paperclips.