This is again a problem of familiarity, or perhaps of naïveté. Roads can have hard to spot potholes, particularly slightly rough roads like that, and people might not be comfortable zipping along them without the knowledge of that.

Far fewer potholes on that than on a typical two lane 60mph road. Not that it’s hard to spot potholes at 60mph.

Familiarity shouldn’t come into it, you should be able to see the road is clear. That road has brilliant sight lines, you can see anything larger than a rabbit from 20 seconds away, far safer Doug 69 along there than 40 along many country roads which aren’t single track, let alone doing 30 in towns.