[ankurdhama]

Why such layoffs have to be abrupt/sudden?

There has to be a series of things over time that lead to such decisions. I think if such things (that can lead to the layoffs) are communicated in time to the people and with full honesty, this can atleast prepare them to be mentally ready for the possible extreme situtation of a layoff.

Do organisations deliberately don't disclose such things to avoid creating any sense of doubts in people?

[gnicholas]

The issue isn't that they have to start abruptly, it's that there has to be a clearly-defined endpoint. That way people can feel secure that the layoff is over, and that they aren't at risk. If you do rolling layoffs, people will live in fear (and the best will find employment elsewhere).

[koheripbal]

Three reasons...

1. Gossip of layoffs causes people to stop working.

2. People email themselves company documents/code/presentations.

3. Some people find other jobs - end up not even being the ones laid off.