The barrier to entry for AI (generative or otherwise) is incredibly low, and mostly consists of harvesting large quantities of training data (which China should excel at, TBH) as well as access to sufficient processing power to process that data. OpenAI doesn't have any magical insight into how a trained model will behave compared to anyone else in the field -- anyone with money could be up to speed in a month or two, tops. The algorithms themselves are well-established at this point, and the "secret sauce" is not very secret either: increase the resolution of your data and add more processing power.
I suspect the reason we don't see the field flooded with more startups (if you don't consider it saturated anyway) is because the business case is just not there. Let OpenAI and others take the risk that there's no pot of gold at the end of the rainbow. If an opportunity presents itself, it would be easy enough to start competing; at least no more difficult than starting today, but certainly cheaper to wait.