I second this explanation. In fact its not just startups but also a lot of big tech companies were rationally taking advantage of the low interest rates to pursue speculative bets/product features. Tech CEOs were being richly rewarded via inflating stock prices for chasing the potential for future cashflows.

When the macro changed, those bets no longer made rational sense.

The silver lining for guys like Jon Bach (as described in the intro) is that with the abundance of free agents and SF/SV office space, it's probably the a great time to form/find an ambitious team and help try to bootstrap the next Google.