Studies show that people can with around 7 items in their short-term memory.
Another truism is that notable deaths come in threes. That may be perceptual bias of some kind, because people die all the time, and how notable any given death is is pretty subjective.
It may be that what we think of as a notable death looms large enough in our minds and in our hearts that our ability to absorb and process them is less than our short-term memory usually allows. These are bigger things than, say, the digits of some sort of ID number (we use to talk about remembering a phone number, which, in the US within an area code has 7 digits, but who remembers phone numbers any more, or for that matter, gets much use from area codes?).
So, I think, we can only process the news of someone's death in smaller chunks.
Today's three, for me, are Chris Cornell, Roger Ailes, and Jan Wolter.
Rock vocalist and lyricist Chris Cornell died this week, at 52.
Conservative political news impresario Roger Ailes died later that same day, at 77.
But Jan Wolter died on New Year's Day 2015, though I'm only now learning of it.