It's one of the hidden tricks of the non-con SoS. Michigan St is probably better than UNC-Wilmington, but UNCW is racking up a big-time W-L record while MSU piddles around in a power conference. The SoS formula doesn't see that MSU is a power team and UNCW is a mid major - it just sees that UNCW's winning percentage is 80% and Michigan St's is 60%. Therefore the RPI sees UNCW as a far bigger help towards the SoS.
Duke and Kansas in recent years have been masters of this trick. They always scout out the best low-major programs to invite for one-offs at home - knowing those schools would be giddy at their one chance, and that Duke/Kansas could feast on their gaudy winning percentage in the SoS.