I don't believe dead deer carcasses had much to to with the spread.
The spread was more about the transport of infected live deer (initially).
Then, dispersing & rutting bucks spreading it further, and further.
One thing that may spread it more than hunters' transporting their carcasses is the spread of prions by vultures that consume the deer killed by CWD. Vultures are migratory and "hunt" both sides of major rivers.
Are most deer that die by CWD (year round) just consumed by vultures & coyotes, then the prions are spread far & wide by, vultures & coyotes?