The pattern here is obvious once you see it. Every single one of these is a suburb near a major metro, not the metro itself. Safe, well-resourced, good schools, short commutes. The things that make cities interesting are different from the things that make people happy day to day.
The 10 Happiest Cities in the US (WalletHub)
1. Fremont, CA
2. Bismarck, ND
3. Scottsdale, AZ
4. South Burlington, VT
5. Fargo, ND
6. Overland Park, KS
7. Charleston, SC
8. Irvine, CA
9. Gilbert, AZ
10. San Jose, CA