Why was eating pork forbidden, but not eating chicken and other animals that consume filth?

Equating pork with other pure animals is something rejected by science and sound nature. Allah has ruled it unlawful and impure in His statement: (for indeed, it is an impurity). The pig's consumption of filth is an inherent characteristic; it is a ravenous, scavenging, gluttonous, foul animal that devours everything with voracity. Eating its meat is inherently harmful and detrimental due to an intrinsic quality inseparable from its flesh. As for chickens and similar permissible animals, they are herbivores, and their consumption of filth is exceptional. If they eat impurities to the extent that it affects their meat, they become "jallalah" (filth-eating animals), and it is disliked to eat them until they are fed [pure food] and their meat becomes good.