There are lots of obvious and not so obvious places where routes can't be calculated, for example, when asking for driving directions across the Darien Gap: "Sorry, we could not calculate driving directions from "San Francisco, California" to "Bogota, Colombia"" Although in theory you may be able to make it across by motorcycle overland, there aren't any roads and as such google maps doesn't plot a route through there.

Kind of insane that there's still a gap there.

It's not insane, it's rather on purpose. In the 1970s there was a huge concern that if proper infrastructure was built, it would cause foot and mouth disease to make its way from South to Central and North America, which stopped the USA's attempt to built a road across it. Within a decade, Panama turned much of the area into the Darien National Park and the UN classified it as a biosphere reserve & world heritage site because of a lot of the other concerns that came up during the attempt.

The epidemiological concerns haven't gone away and there isn't much interest in building across the gap.

> In the 1970s there was a huge concern that if proper infrastructure was built, it would cause foot and mouth disease to make its way from South to Central and North America

That's fascinating!

Wikipedia shows that the disease is nearly eradicated in South America:

https://en.wikipedia.org/wiki/Foot-and-mouth_disease

I suppose there still wouldn't be an economic incentive to build a road when there are two large bodies of water on either side?

I read somewhere it was because they wanted to avoid the drug smuggling. The foot and mouth thing is new to me, it sounds odd.

I’ve seen various warnings on walking or biking directions, as well as on driving directions using ferries or toll roads, or crossing borders.

So they are neither categorically opposed to warnings for any of the reasons you mention, nor are there technical difficulties. I guess the case of roads that are dangerous just happens to be extremely rare.