In my mind there are really three dimensions they can differentiate on: cost, speed, and quality. Cost is hard because they’re already losing money. Speed is hard because differentiation would require better hardware (more capex).
For many tasks, perhaps even a majority right now, quality of free models is approaching good enough.
OpenAI could create models which are unambiguously more reliable than the competition, or ones which are able to answer questions no other model can. Neither of those has happened yet afaik.