Why did Polybius criticize historians who relied on sensational stories?

Polybius criticized historians who relied on sensationalism because he believed they confused the purpose of history with that of tragedy. While a tragic writer seeks to thrill and charm an audience through plausible language—even if the events described are false—Polybius argued that the true object of history is to instruct and convince serious students for all time through the record of real facts and speeches.1

He contended that sensationalist historians often attempted to astonish readers by inventing probable utterances or exaggerating the consequences of events. Furthermore, he noted that writers of narrow, monotonous monographs were often driven to magnify small matters and transform unimportant incidents into momentous events to compensate for their limited subject matter.1

For Polybius, history was essentially pragmatikē historia (pragmatic history), which must focus on political and military matters to be truly profitable. By prioritizing truth over the desire to beguile the spectator, the historian provides a sound education for political activity and helps readers learn how to face the vicissitudes of fortune.1