I think they also do that. This is just to give people the initial news as soon as possible, and without ambiguity or speculation as it takes days to percolate through if you did it 1:1.
They did it one by one, and it took roughly a full day to get through everyone. The whole company was on pins and needles- even those who were doing well couldn't think about anything other than wonder whose names and faces they wouldn't be seeing around the office anymore.
As an individual, I empathize with the emotional difficulty of an impersonal mass layoff. However, having seen the flip side, it's a whole lot worse to spend 8 hours wondering when the hammer is going to drop on you. Ultimately, it's better to get it over with quickly, imho.