When a downturn like this happens, the Federal Reserve lowers rates to encourage spending. But at the same time, people are less likely to hold corporate debt and instead hold cash. People are less likely to hold corporate debt because the corporation has less revenue to service its debt. In the case of a (highly) public company which doesn't have profits, if Uber were to try to sell bonds, the spread over, say, treasuries, would probably be above 8-10%.

In other words, corporate debt isn't priced according to lowered rates. It's priced according to what bond investors would need to be paid in order to adequately compensate for the risk of Uber going bankrupt.

The only way the Fed would help would be if the Fed bought Uber's bonds, but that would require Uber to be investment grade, which would be laughable, or a "fallen angel", a company which was investment grade before the crisis but has since been downgraded.