I'm personally thinking it's sad such resources and effort are expended over something as frivolous as a dating app. If there are significant irregularities it's better to just fine them a couple of billion later. Better for the wallet, too.
There's a public safety issue here: dating requires interpersonal negotiation for personal intimacy with consent, which in turn implies that a dating app needs to be "safe space". Facebook is notorious for leaking personal information to third parties (typically but not always advertisers). I have no knowledge of specific risks associated with Facebook's dating app, but the precautionary principle should apply in those cases where personal safety is at risk, and the sheer scale on which Facebook operates means that a dating app backed by the big F needs oversight.
Luckily, GDPR FTW.
Dating apps handle data related to what many regard one of the most intimate parts of our identities. You and me, we might not care if our dating habits were exposed, but other people do. So dating apps needs to show that they're up to par.