This theory has several prongs:
1. Each city is linked to a specific Herald. I have no evidence to support this, it just seems reasonable.
2. Each Herald holds the "key" to the Oathgate in their respective city. Again, no evidence (this will be a recurring theme).
3. Those keys are Honorblades.
4. One of the Heralds broke their oathbreaking agreement, went back, and gathered up the blades. (I'm assuming Jazrien for no particular reason)
5. They then locked all the Oathgates (excepting Taln's, Stormseat), possibly to try to hide the Heralds complicity in breaking the oaths.
6. They then destroyed Stormseat to avoid any KR from investigating possible differences between betrayed, unusable Oathgates and that of Taln, whose gate stopped working when his blade left the physical plane.
Some indirect support from the Listeners' knowledge that THEY did not shatter the Shattered Plains.
7. They then formed a Cult to keep the Honorblades secret, thus insuring that the real reason for the gates failing went unknown.
8. Profit?