I don't understand. A bunch of cities defected after Cannae. Livy gave a list:

• Apuliani
• Atellani
• Bruttii
• Calatini
• Campanians
• Crotoniates
• all the Greeks on the coast
• Hirpini
• Locri
• Lucanii
• Metapontines
• Tarentines
• Uzentini

Are you asking why the Latins didn't defect?