Why did ABC show a Republican PAC ad of Alexandria Ocasio-Cortez's image on fire during the debate?

The Cut

"Republicans are running TV ads setting pictures of me on fire to convince people they aren’t racist. Life is weird!" the U.S. representative from New York tweeted of the ad showing her official congressional portrait on fire. The ad puts the congresswoman at risk, says Sarah Jones, pointing out that she and her "squad" have already received a high number of death threats. "ABC grants undeserved legitimacy to ideas that make her a target," she adds.