I had similar emotional reactions to these events, though switched around. At age 21, I felt and otherwise grasped the significance of 9/11, whereas at age 40, the storming of the Capitol (though I've spent hours reading about its significance) never hit me on a gut level. I believe I know the reasons for this.

9/11 came totally by surprise--I remember what a beautiful day it was--and I was in a city between Boston and New York, so I was physically looking upward to watch for more planes, because no one could assure us that we weren't under attack and that tomorrow wouldn't be worse. I had to contact my family and figure out where everyone was, and everyone else around me was doing the same. (Most of us didn't have cell phones yet.) I watched many video clips, as most Americans did, trying to piece it together on the factual level and the geopolitical level.

This year, at age 40, I am living outside the United States so I felt a bit removed from the elections in that sense. I was paying attention to the election news, and I expected that there would be election violence roughly on this level; in October, I wrote a whole series for Medium about the possibility of a coup, and I was surprised when November and December were quiet. January 6 itself did not surprise me. Also, because I didn't watch video clips of the Capitol riot, for several days I misunderstood the size of the crowd--I had been imagining it as about 1% of its actual size (hundreds, rather than tens of thousands).

So, that's my theory of a couple possible reasons why some major news events hit the gut more strongly than others: whether, to any particular person, the event feels expected/comprehensible or surprising/incomprehensible, and whether the person is immediately physically present in a risky area or watches visual images of the violence, as those may access the deeper emotional parts of the brain.