[mijamo]

This sometimes happen but is not the norm. The problem with this approach is the long uncertainty for EVERYONE while the decision is made, and if many managers are involved it's basically the same as it being public information. In a lot of recent layoffs everything was decided in small committees so that it can go really quick between announcement and effect.

Also evaluating employees is really really hard when it is creative / intellectual work and most of the time personal affinities override any decision from managers so that is not ideal.

[Volundr]

Especially because the managers they'd delegate this too are also potentially on the chopping block. In my experience the larger the layoff the more likely it's a small committee of upper level management and HR figuring out who goes.