Border guards have always had extreme amounts of discretionary power over who enters the US or indeed Canada. In the past they would just turn you away. It happened often enough for Canadians, or people on visitors visas to Canada, wanting to visit the US.
The difference now is that someone who would just be turned away 5 years ago is now much more likely to be arrested and sent to an ICE detention center and not allowed contact with lawyer or family. It would appear there is some kind of quota system at work where border guards will pick the easy targets that in the past would just be refused entry. Because they want high numbers for the ICE detention system.