The system doesn't randomly permit this. DL has made a conscious choice to set the MCT so that this connection can be sold. Why? Because there are people who want short connections
Why? Because there are many people who book short connections because they want short connections. If, as a passenger you don't want a 35-minute connection, you should not book it.
Or, given that there are three carriers offering nonstop ORD-NRT service, I'm not sure why OP wants to fly to DTW to catch a flight to NRT in any event.