- A lot if them are not profitable. - They don't know how long this will last. - Many planned on growing into profitability over n months and expected they could raise more money if needed. - Now, there is no growth for many and contractions. - Investment money is drying up - they might not have 2 years at their current burn rate to get to profitable status.
In the end, it can be about survival. Their pre coronavirus burn rates are not sustainable. Of course, for some, it is also a continent way to shed staff who appear to be underperforming, freeze raises, and ask more of their employees.
For many (even unicornish) startups the funding is released in tranches, usually tied to certain performance metrics. With drastically reduced revenue, new customer flow all dried up, and even marketing result graphs simulating nosedives, there aren't that many milestones you could hit.
If [enough] performance milestones are missed, company's next batch of on-paper funding pot may not be released.