Yeah but this year the number of people working from home that would connect to slack directly at the beginning of their work day must be much much larger than the other years

Another small but potentially relevant detail: Not many people vacationed, so more people would have returned to work at standard times. Many people travel over holidays for example (usually) but this time around in many places it wasn't even an option. Other people extend their holidays to relax more, but I don't know any people interested in staycations in their house. We've had enough of it.

But also smaller because much fewer people went on a long traveling vacation away from laptop.