Fair question, as is: why did Sherman burn 'from Atlanta to the sea'; or why did the British burn Washington?
Civil wars and rebellions and their aftermaths somehow seem to have a way of being 'people killing their 'own' people'...can't imaging how that comes about, but it may be an answer to look for here. *<];-)
I also read the original, and then, as well as now, am intrigued by the 'clay bullets', as if the Middle East doesn't have enough stones to use. Never seems to be any shortage for the Palis to throw at Joooz; or Muslims to use for stoning women.
Quite simple. Standard shape, size and weight from a mold increases accuracy and thus lethality over random stones. Lead "bullets" for slings, when those became available during Hellenistic times, worked even better.
Clay bullets are lighter than stones, and more reliable (because they are manufactured, they have a regular shape and size). Sling weapons were enormously popular.