This implies that the interest rate reduction counter-balances the reduction in future cash flows. In an economy with 15-20% unemployment and entire industries

This implies that the interest rate reduction counter-balances the reduction in future cash flows. In an economy with 15-20% unemployment and entire industries on the brink of destruction ( airlines/travel ) this is not a given. If the 5-10 year revenue projections of air-travel are 1/5th of the pre-covid economy, then a small change to cost of capital won't allow you to continue investing as if nothing happened. The risk inherent to Google's bottom line from long-term structural unemployment and lower ad-revenue should outweigh even a 0% cost of capital.