Religion is complicated and built up over thousands of years. I am sure some rules are to designate an in-group/unity, some are based on the best belief at the time for the public good, some are probably arbitrary dictates from whomever happened to be in charge at the time. I think it would be a mistake to lump all the rules together (just as it would be a mistake to lump all of our modern laws together). Some are also self obvious, for example, i believe one of the kosher rules is dont eat animals that have been poisioned.

As far as pork specificly - i imagine nobody really knows, but there's some speculation at https://en.wikipedia.org/wiki/Religious_restrictions_on_the_...