I think Hebrew dietary restrictions may be more instructively viewed as a mechanism to enforce group cohesion than as a primer on suggested health practices. It is difficult to mix with other groups when you cannot eat with them. Matrilineal line of descent serves the same function. Children fathered by in-group men with women outside the group are simply excluded, while in-group women face censure for the same behavior. There are structural reasons why Jewish culture has remained distinct in diaspora, while many other disjoint populations are absorbed by host populations over time.
Longstanding practices are often multiply-determined, and the relative balance of benefits may change according to the situation. (In high-sanitation environments, the rules help enforce cohesion/segregation; in low-sanitation environments, the rules provide protection from endemic parasites.)
Agreed, there are always reasons for specific decisions. In the three cases you've mentioned, the banned flesh is from animals that are carrion eating scavengers.
