There are a variety of reasons for the following:
a) why this particular flight had to divert
b) why they choose to return back to DTW
As others have said, not all airlines/operators, equipment, or flight crews all have different operational specs, navigation equipment, and qualifications to land in certain conditions.
If an AA A320 was able to land, it doesn't necessarily mean a 9E CR2 could get in.
That said for a diversion, a lot would depend on what is feasible to do at that time of the night, the remaining duty time of the crew, and ability to accommodate passengers.
While a diversion to PIT may have been closer, the crew may have then gone illegal / out of duty time and then be stuck in PIT for the night, now with an out of position airplane and crew. When in fact returning to DTW could mean the ability to get a relief/reserve crew, accommodate passengers on flights in the morning, and/or have the airplane back in position for the next day.