FYI. From support:
The WIS rankings use the Coaches and Press rankings as a starting point and then modifies each team's ranking based upon home record, road record, neutral record, scoring margins, and strength of schedule.
With all of these factors considered, both Michigan and Florida edged you out. The biggest reasons for this are your SOS compared to the other two and the fact that Florida's loss was at a neutral site. Your scoring margin was better than Florida and helped you out but it was not enough.