Explain this to me

It's a fantasy. That may surprise you but once that sinks in hopefully you'll feel enlightened.

You left out a vital detail that changes your whole point. An ugly, possibly rabid, dog falls out of the sky AND ATTACKS YOU. Your initial reaction is to chase it down and kill it...BECAUSE THE DOCS NEED THE HEAD TO TEST WHETHER IT HAD RABIES. AFAIK there's still no test for rabies in humans until the disease has spread so much it's going to kill you.

But, of course, that wasn't what these city boys were thinking at all. First, that clearly wasn't any dog, and the body of a strange, exotic animal could be worth thousands of dollars. Second, by attacking their gang leader, the creature disrespected the gang, and respect is one of the primary concerns of low-status groups. We all crave what we don't have, right? So, by their rules, they had to kill it or lose face. ;)