Some animals are meant for foods and some are not. Shellfish like shrimp, crab, lobster are bottom feeders and eat the waste of other animals, as to why they are unclean and full of toxins.
Pigs have a poor digestive system and their toxins get stored in their fat, that is the main reason a pig is unclean and a cow isnt.
I know Im about to hear all the excuses from the usual folks on here, but its common sense and God created us, so he should know what is food for us and what isnt. He wouldnt tell the children of Israel, not to eat certain foods because they are unclean and then give Christians the green light to eat that same food, as God would be contradicting himself. God isnt schizophrenic to the point where for Noah anything is clean, for Moses you cant eat unclean and then after Jesus you can eat unclean again, that would mean God changes his mind about the issue every 1500 + years and it confused with his own decision.
Take Peters vision in Acts 10
Acts 10:10-14
10 Then he became very hungry and wanted to eat; but while they made ready, he fell into a trance 11 and saw heaven opened and an object like a great sheet bound at the four corners, descending to him and let down to the earth. 12 In it were all kinds of four-footed animals of the earth, wild beasts, creeping things, and birds of the air. 13 And a voice came to him, “Rise, Peter; kill and eat.”
14 But Peter said, “Not so, Lord! For I have never eaten anything common or unclean.”
Jesus has been dead now for probably a couple of decades and Peter still isnt eating unclean foods, because they knew the dietary laws were not canceled, so when you get to Acts 10:28 the vision was revealed for this to be about Gentiles and not referring to them as unclean.