One of the yesodos of HCT, is that you are usually traveling through a hub, as that is where most connections happen.
For example, the reason you were able to find the way back flying US is because PHL is a hub of their's and therefore you have a "stopover".
To fly to DTW, using HCT, you need to find an airline that has a hub in DTW, aka DL, not US.
(The exception is spoke to spoke, but that kind of routing is far less common and usually more expensive.)