Town criers spread news because literacy was low in preindustrial cities [causal]
Given the lack or minimal use of the printed word and given the generally low levels of literacy among the populace, the public space of the preindustrial city understandably enough was further enlivened by the distribution and collection of news. Town criers relayed elite pronouncements to the citizenry, warned of fires or other dangers, and spread news of interesting, if mundane, events: … The town crier [in medieval Prato] ... hurried from one street corner to the next, to spread the day's news: births and weddings, and deaths, bankruptcies and emancipations, lists of lost property and lost cattle, even applications for wet nurses-while more important official news was imparted by three trumpeters on horseback, dressed in the colours of the commune, who blew a treble blast on their trumpets before announcing the sentences of the courts of law-banishments and fines, and sometimes executions.
XREF: Connects to the broader sociology of pre-modern communication and oral culture versus the printed word.
Lyn H. Lofland, World of Strangers_ Order a…, loc. 196