Because people like the dinosaurs. But why cannot we get enough of them? Elephants are big and smart, but there are almost no movies about the elephants. Ditto for extinct, large land mammals: the sloths, the armadillos, the pangolins. These were not only giant, but also exotic looking. Not good enough. Indricotherium was 10-20 tons, as big as a midsize sauropod dinosaur; still, no movies. Dinonyus, the Hyaenodonts, Uintatherium were impressive mammals, scary as scary goes, but few have even heard their names. Is it something special about the reptiles? Not really. Postosuchus was the top predator of the Triassic and many of the archosaurs and rhynchosaurs were frightful meanies, striking in their appearance, but these reptiles are not loved, whereas the dinosaurs are. The dinosaurs are scary alright, but there is also something attractive about them. Even the medieval dragons had princesses to attend to their needs...
I am wondering why. Large animals, like dinosaurs, have a particular problem: skin parasites. The familiar sight of the oxpecker bird sitting on a rhino and cleaning it from fleas and mites is the general rule: for every big animal, there is a small animal specializing in cleaning its skin and cavities; it is the textbook example of mutualistic symbiosis. Egyptian plover cleans the teeth of the Nile crocodiles from the leeches. Hippos, zebras, giraffes, elephants - all rely on birds for cleaning. The dinosaurs had vast expanses of exposed skin with many folds; the meat eaters had rotting flesh between their huge teeth. Their parasite problem should've been overwhelming. Who cleaned them? Small dinosaurs? Birdlike dinosaurs? Birds?
The life of the mammals under the dinosaurs is pictured in the darkest terms. Supraficially, this makes sense, but there is, obviously, one niche that was open to the mammals to escape the harassment: cleaning the beasts. The cleaners are tolerated, which may explain how some of the mammals made it through the bad times.
Our evolutionary ancestors were insectivorous proto-primates; it is believed that they assumed arboreal way of life somewhere at the end of the Mesozoic. However, the presumably arboreal adaptations would be the same adaptations one would need to clean large animals, like the dinosaurs. This is a very old problem: was the arboreal way of life primary (the arboreal hypothesis) or visual predation had evolved first (as you can live in the trees without our primate adaptations). The molecular clocks suggest the proto-primate branch evolved around 85 Mya. Our own order branched off these mammals about 63 Mya; the lories and the lemurs branched off about 75 Mya. Our ancestors have been a nocturnal, tree-living creature weighing about 1-2 pounds, with grasping hands and feet, also used by the infant to cling to the mother's fur. It probably had large forward-facing eyes for stereovision and a shortened snout (reflecting a reduction of the anterior dentition). It would have inhabited tropical/subtropical forests, feeding on a mixed diet composed mainly of fruit and insects. Like humans, it probably had a slow pace of breeding characterized by heavy investment in a relatively small number of offspring. http://www.sciencedaily.com/releases/2002/04/020418073440.htm
Imagine the scenario: around 90 Mya an insectivorous mammal betrayed its kin (that served as snack to the dinosaurs) and hit on a symbiotic relationship with the mortal enemy, cleaning their skin from the parasites; that is, doing the same work that the modern birds are doing. The adaptations to the "arboreal" way of life were, actually, the adaptations to doing this job, but it makes sense that the animal stayed some time in the trees, if only to avoid the predation on the ground. The niche was open and occupied, as the birds were still primitive. Then the disaster struck about 65 Mya: their symbionts all died out; actually, all large animals died out. Now our cleaning animal had to switch from its customary cleaning jobs to fully arboreal way of life. The modern primate was born. Today, nothing betrays this special role that our ancestors played in the dinosaur dominated world of the yesteryear except for... except for this peculiar love mixed with fear.
Why do we love the dinosaurs?