Why are scientific facts denied?

Ken Ham - Biblical literalist and Young Earth creationist;
Founder of the Creation Museum

Maintains that humans and dinosaurs coexisted.

Factual realism - the science:

Non-avian Dinosaurs went extinct 65 mya.

How it is known:
Global distribution of iridium isotopes in
65 mya KT-rock layers.
Loss of diversity in fossil record 65 mya.

References:
Alvarez, LW, Alvarez, W, Asaro, F, and Michel, HV (1980). Science 208 (4448): 1095-1108.
Hildebrand, Alan R.; Penfield, Glen T.; Kring, David A.; Pilkington, Mark; Zanoguera, Antonio Camargo; Jacobsen, Stein B.; Boynton, William V. (September 1991). Geology 19 (9): 867-871.
Pope KO, Ocampo AC, Kinsland GL, Smith R (1996). Geology 24 (6): 527-30.
 

Oldest known Homo sapiens fossil of an anatomically modern human is ~195,000 years old.

How it is known:
Potassium-Argon isotope dating of volcanic ash found just below the fossils;
geological layering of the local rock

Reference: McDougall I., Brown F. H. & Fleagle J. G. Nature 433, 733 - 736 (2005).
Difference between oldest humans and last dinosaurs:
 

The difference is significant (~64.8 million years).