To be fair, FLoC had signifient issues and could be used to fingerprint users. Google's whole point of FLoC was to get rid of third party cookies, to stop sites from fingerprinting users and tracking them throughout the web, so FLoC didn't really solve the problem in that regard. With Ad Topics, only a limited subset of topics are presented to the advertisers, and fake data is injected, making that fingerprinting less likely.