You're missing servers. Power9 is cheaper but similar performance to Intel Xeons and Google has invested quite a bit into using Power servers (although we don't know if they actually do).
I'm sure all the effort Google put into being able to compile google3 for Power resulted in significant price concessions from Intel, which I imagine was the point of the project in the first place.
Sorry for the jargon. google3 is the name of their perforce repository that contains all of their backend code, everything that runs in their datacenters.
