MSP-ORD is operated daily with 10 flights, all utilizing mainline aircraft with at least 100 seats per aircraft (most have 124 or more seats). That's a lot of seats each day.

MSP-DTW is operated daily with 16 flights, all utilizing mainline aircraft, many of which are 757s with at least 182 seats per flight. That's a lot of seats each day.

You can search by schedule on NWA.com and select flights that only have one connection (or no connections seeing as you're in MSP). You may pay more for them, though. That's the consequence of having all that frequency of non-stop flights. You pay more for being able to choose from that many flights per day.

Good luck.