At the end of the day, shipping by sea is much more efficient than shipping over land, and the narrow spit of land connecting North and South America has lots o

At the end of the day, shipping by sea is much more efficient than shipping over land, and the narrow spit of land connecting North and South America has lots of sea access, including car ferries to connect the road networks. So you wouldn't expect a road connection to be developed if it's super expensive given that this more efficient alternative already exists, and, well, the road connection is super expensive.