What will happen to a channel if someone uses Pirated stock images and videos from popular websites in their videos?

My friend has a YouTube channel where he creates voiceover videos with original audio. However, he uses pirated stock images and videos from websites like iStock, Shutterstock, Storyblocks.. you name it... without a license. Despite this, his videos don’t get flagged when uploaded to YouTube, and he has never been asked to provide proof of licensing for the stock footage.

Do these stock media websites issue copyright strikes? What are the risks involved in using unlicensed stock footage? I'm new to this and trying to understand the potential consequences.