Google spends all that money on "taking the everyday problems away" from its engineers so they can spend their time in the deep thought needed to really think about a problem before writing code to reflect their solution.
The fucking bullshit MBA approach of "look busy" is what Google and other tech companies have disrupted through the years.
You're absolutely right in the last statement that this is a hedge by the CEO to prep for uncertainty. I would take that argument a bit further and claim that this is also a hedge to insulate their recruiters and pretty much everyone with connections in the bay area from freely referring candidates from the other sinking ships such as Facebook, Snap and the rest that would dilute culture.
He seems to be giving cover to everyone with the hiring freeze so that they can more readily control the influx of job applications that is happening right now with these other large employers laying of talent very similar to the cohort working at Google.