Because we already see firms competing effectively with OpenAI.

There is as yet no indication that AMD can match Nvidia's execution for the very good reason that doing so is extremely difficult. The head start is just the icing on the cake.

A head start is a moat iff you can't move easily from the leader to a competitor that catches up qualitatively; nvidia’s headstart against AMD is a moat to the extent that you can't just take the software written against NVidia GPUs and run it on AMD if AMD catches up. (That is, being currently ahead isn't a moat, but it can impose switching costs which are.)

Taking code that runs against one hosted LLM and running it against a different backend LLM is... not generally a big deal. So OpenAI being ahead—in the core model, at least—is just being ahead, its not a moat.

Not all industries or product segments are equal is the obvious answer. The point here whether one agrees or not is models are easier to catch up to than GPUs

Anyone can make an LLM. There are hundreds of choices in the market today. Many of them are even open source.

OpenAI brings absolutely nothing unique to the table.