[defrost]

They had no advance warning of what to expect:

    The moderators say they weren’t adequately warned about the brutality of some of the text and images they would be tasked with reviewing, and were offered no or inadequate psychological support. 

As noted above and below, it wasn't just text:

    The 51 moderators in Nairobi working on Sama’s OpenAI account were tasked with reviewing texts, and some images, many depicting graphic scenes of violence, self-harm, murder, rape, necrophilia, child abuse, bestiality and incest, the petitioners say.

> because I truly cannot imagine

You're not alone, there's likely a higher than normal percentage of HN'rs that have difficulty imagining how other people react and feel.