"no one" is not accurate, but a lot of people do have a tough time accepting this, as denial is not just a river in Egypt. The reasons for this vary from individual to individual. For example, some people are so obsessed with flying a few men to Mars that they do not want to see space money spent on anything else.

An eyeball estimate based on quarry usage is that the fatality rate was 90-95%. In North America people survived in the region from Big Bone Lick to about Florence, Alabama (Shawnee, Cherokee, Tuscarora), in a pocket in New York around Oswego (Five Nations), on the Pacific Coast of today's Canada (Lenape), and in the northern Rocky Mountains (Sioux).

The exact number and locations of the impacts are being worked on, with NO HELP FROM NASA, but instead obstruction by David Morrison, as the impactor(s) were comet fragment(s). What we do know from the distribution of cometary impactites is that the event was massive, and to me the Alberta structure that I linked to earlier looks about right for one of the larger pieces.

Aside from the immediate blast effects, which were massive and which appear to have extincted the mega-fauna instantaneously (no over hunting) , my guess is that the impacts affected the Pacific Current, and that led to climate change -the beginning of the Holocene, with flooding from the melting ice.

In any case, the fundamental points are:
1) DENIAL
2) NASA DENIAL, and the lack of research money