Because there are suburban coyotes that are habituated to dogs and humans. They have the potential for very different cost/benefit ratios in terms of what they do.
A rural coyote that does not stalk livestock may simply see humans and domestic dogs as "not-food", and "threat", and there's zero point in engaging them. A suburban or fringe-rural coyote that's snacked on a small dog, a few cats, gone through garbage, or finds food in proximity to human activity, noises/scents may be very different.
^^ This, plus eleventyone.
Also, coyote in different parts of the country have different degrees of hunger/aggression.
Desert 'yotes are more likely to tackle larger game than 'yotes from wetter parts of the country, where small game is plentiful.
Coyote varminting has a distinct effect on white-tail populations in AZ. The more 'yotes you bag, the more deer there will be the following year. That tells me that coyote quite routinely prey on deer, here. That conditions them to prey on other ~100 pound animals.