Autonomous highway driving is not easier than urban, if anything for the typical Lidar-based approaches it's much harder due to limited Lidar range and very long stopping distance requirements for trucks, plus the fact that a bigrig can cause huge amounts of damage in any accident.

The various pure-play L4 companies that pivoted to trucking due to its alleged relative ease were simply exploiting layperson investor bias to rake it in (or possibly even had a similar bias due to lack of expertise). It's an open secret that Embark had virtually no chance to go to market, even in a good macro environment.