What do we learn from "Ga'on Siv'as Lechem v'Shalvas Hashket"?
Radak: Why did it have Ga'on (pride)? Because it was satiated with bread and serenity. Shalvah is Samuch to Hashket to show the great Shalom that they had. Siv'as is a noun. Or, it is an adjective, with the same grammatical form as "Shiflas Komah" (17:6) This [satiation] was a reason for its serenity!
Was their only sin not supporting the poor?
Malbim: For this sin, Bein Adam l'Chavero, they are worthy to be punished. The Sechel counseled to intentionally be crooked. They did not do so amidst difficulty - Sedom was Ga'on Siv'as Lechem! They did not guard storehouses of grain for times of war and siege - they had serenity! They did not support the poor due to their evil etiquette and laws, in which [the poor] cannot live. Their etiquette was not to before the poor or one who lacks bread.