I think a lot of it just has to do with how humans normalize things.
My dad grew up in Europe during WW2 and I asked him what it was like, and he said it was like having five 9/11 events, every single day, month after month after month.
But eventually, even with all that chaos, he said there was a normalization that happened and life went on.
If 9/11/01 wasn't a singular event, but rather a daily event that went on for 12 months straight, eventually it wouldn't be very big nightly news, because the shock and awe effect of it would have warn off. It would have just become a normal way of life.
And most important not to forget - the entertainment industry (news, Hollywood, sports, etc) needs novelty to attract viewers. The human brain seems hardwired to be attracted to new things.