Rockfall is very common. Its how climbable faces are formed. And climbers follow routes that are on natural weaknesses in the rock (flakes, cracks, etc) so rockfall is an accepted hazard. However deaths by rockfall are much less common than actual rockfall events. Most deaths due to rockfall are probably smaller size events, a fall on gear might put pressure behind a weak flake or a small partially detached boulder might come loose. Small rockfall events from climbers knocking things down from above can hurt or kill people below, I was involved in such an event several years ago on the east coast. But I would hazard a guess that something of this size that causes a death are more rare, I recall reading that there have been only something like 20 deaths due to rockfall in Yos in the last 150 years (the link below states 16 since 1857). And larger rockfall events like this probably more typically happen in the spring or late winter after water seeps into the weaknesses in the rock, freezing during the winter and expanding and further weakening the rock followed by a thaw cycle which allows the rock to move more easily.
Further details about rockfall in yosemite
Sciency Stuff from the NPS about rockfall
I like this chart on rockfall events and time of year although its a little hard to tell and I wish it was interactive, you can see that there are many more large scale events during the winter
Fun fact- if there is a rock fall event (granted probably this doesn't apply to something of the magnitude of the recent fall) one should run TOWARD the rock wall. Most people intuitively will run away from the wall, which is the most dangerous as rock falls away from the wall, but your best bet is to run toward the rock wall and crouch against it as this will offer the most protection.