If a piece of creative work would not have existed without the prospect of financial gain, it's unlikely to be very good. Society would not have missed out on much if some famous author published only their first 3 truly inspired works, which they wrote to satisfy their creative urge, but not the 20 potboilers that followed.
We need to distinguish discoveries, inventions, and creations. Discoveries cannot be protected by patent/copyright. Inventions can and should (within reason). Creations might also deserve protection, but the incentives argument here is much weaker IMO than in the case of inventions.
Ironically, the NYT, which prides itself on being a neutral and objective purveyor of facts, isn’t challenging OpenAI for using the factual elements of its reporting in training data. Facts, being discoveries, aren’t copyrightable. Instead, they are focused on the part where journalists exercise "creative freedom" – the specific wording, narrative, and "spin" journalists put on reported facts. Let's apply the incentives argument to this context: is it clear the world would be a worse place if NYT journalists lose the incentive to exercise creative freedom in their news reports?