Why? Intel can compete with Zen more easily it can also always rebound even if Google does go with Zen.
But if Google switches to an entire different eco-system dragging it back into x86 won't be easy because all of their platforms are built for a completely different architecture.
Next generation uArch from AMD. Which promise 40% IPC improvement . Again it won't be as fast as Intel, but at least AMD is within Reach for a price war, where as now even if AMD is 50% cheaper it makes little sense to use them.