I work in IT, where we lose a lot of tribal knowledge when someone in our department leaves.
I've seen this happen at every place I've worked.....
IT person leaves: we find out about it via word of mouth, usually either just before their two weeks is up but usually find out after they've left.
Someone in management leaves: company wide email as soon as they put in their two weeks.
It boggles my mind. It's like they don't want us to know someone is leaving or has left.
Sometimes that person was helping me on a project. I reach out for an update only to find out they left weeks ago.
Makes zero sense.