Old roads that formed on old paths are much more stable because people went where the area was dry, and then dirt roads were stable and didn't move down or cause rain erosion. The generalizing phrase, that terrain is just an obstacle that should be plowed through, is laughable. People lived very well without retaining walls and without such huge excavations, until transport engineers decided to please cars, and not slow them down, or not make them go too steeply.
Same for the sentence about buildings. There are plenty places where slopes are taken adavtage of. In Stockholm, there are some houses that have +2 storeys on one side, and entrances to 3 storeys from different sides. In my town, a mall built in 1960s has 2 storeys, the top one can be entered without steps at all. In Finland, they used sloped ground to build stadiums, and even to make basements with windows.
People like parks with slopes, children like to ride sleighs in winter on them. The most stupid thing you can do near housing is a flat surface and a concrete retaining wall. That generates more problems than benefits: the wall may float, it may create new concentraded areas of water running on the surface, and mini-waterfalls in rains. This never happens with natural slopes, because with grass they're very stable at 3-10 degrees, unless you concentrate water runoff on them.
Finally, the place becomes completely uncomfortable to stay at. It's pretty normal to lay down on a grass on a slope. But unthinkable if there's a retaining wall above you.
Unfortunately, nowadays I see the architects and clients prefer not to think and adapt to terrain, but just bulldoze the ground.
Otherwise, yes, there are engineering solutions to making retaining walls and making them stable.