Two weeks seems like a really short time to have any effect... aren't the open positions and people applying for them going to be almost identical two weeks later?
My interpretation is that they are taking time to reassess their open positions, and the list of positions will be smaller when they reopen hiring.
Until further notice is more palatable after a short notice.
This might have less effect on direct hiring than on attrition. It's a signal that the next review cycle at each of these companies will be absolutely brutal. As a result, both the truly marginal and the good-but-undervalued employees will be flying for the exits. Net effect might be greater than if only hiring had stopped.
If Google and mega cap gang are scared and slowing hiring where are their current employees going to go that doesn't have a greater risk of layoffs?
Probably nowhere. There are probably boring industries that might be more stable but they would likely involve a pay cut so expected value probably suggests staying put.
Yes, there might be a pay cut, but half of that pay cut's already there (via reduced stock prices) and the rest will come anyway for someone about to be PIPped out. Expected value then is zero. There are still other companies both in and outside of tech - possibly including the one we both worked for - that are still hiring and offer pay that's still good by most standards. There's contracting, which in past downturns has often picked up a bit to fill gaps left by hiring freezes. Also, for someone who has been pulling down GAMMA pay for even a few years, "nowhere" is very much an option either temporarily or permanently. I'm pretty glad to be "nowhere" myself. ;)