A lot of the very big companies are quite reluctant to start layoffs if they think the situation can be survived for a few months. They don't want to be seen as evil firing-their-contractors, people-as-expendable, etc. They are an easy target as "big corp".

But if they can see this is going to go on more than the end of 2020, they will start having to confront the need to layoff people seriously. Interestingly, the more certainty they have about how bad it is, the sooner the layoffs.