HD Maps don't need to include every single object. That would be foolish both in the time and resources required to create such detail and the fact that it would increase the chances that your map would be wrong. Rather, maps just need to include the important fixed landmarks such as the road itself, overpasses, signs etc... But you would not include objects like construction cones.
HD Maps are also not your primary source for driving for the obvious reason that you don't want to crash the car if the map is wrong. Rather, HD maps serve as a back up system. For example, if there is poor visibility such as fog, where your cameras will struggle, the self-driving car can fall back on the HD maps for confirmation of where the road is for example. The primary source will be your sensors such as cameras, lidar, radar etc... They are the ones that actually guide the car.