If big game hunters must dispose of carcasses properly, why isn't this also the standard for salvagers, which don't have to take all the animal if they don't want to?

That is a good question.  We ask that salvagers pick up the animal they wish to salvage and haul it away to process.  We also ask they put safety first when salvaging.  Proper disposal of a carcass is always recommended once you take it into possession.  However, you bring up a good point that people don't always use safe and common sense practices when salvaging a large animal.  Perhaps it is something we need to revisit in our salvage rule.