The expected net present value[0] of their cash flows is not down 50% since they're expected to recover from the downturn. They're already down quite a bit to account for the downturn, and they might go down further. Or start going up. Depends on how people value their cash flows. If you think that the market is underestimating the impact of this on google, sure you can bet against them, but the institutional mechanics of shorting make it quite a bit riskier than going long, and, well, if you're wrong on what the market price will be, won't turn out well.

[0]https://www.investopedia.com/terms/n/npv.asp