Why did Zillow’s settlement require Redfin rental listings to return?

Zillow settled the FTC's antitrust lawsuit over the $100 million deal in which Redfin had agreed to exit the internet listing service market for apartment rentals for up to nine years [1, 2]. The FTC argued this arrangement unlawfully shut down competition in that market, so the settlement unwinds the deal and brings Redfin's rental listings business back [1].