Why did heresies appeaar more frequently during the 13th and 14th Centuries?

Heresies were present even from the time of Christ and shortly after. In his letters, the apostle Paul even addressed one of the gnostic heresies. The same heresies have repeated through history and are even present today under the names of other religions in the last few decades. It may have seemed like they were more common by the 13th and 14th centuries but they have always been common.