Eventually the top labs are going to collude and simply not release their best models to the public (if they aren't doing that already).
I suspect the top labs will come up with a business model that doesn't involve handing out their secret sauce for everyone else to reverse engineer. Perhaps restricting their top models to select high paying government/enterprise contracts. Or maybe a bespoke "describe the problem and we'll solve it for you" type service.
OpenAI doesn’t even know how their model works. Nobody knows how LLMs work. So it’s not like it’s technically difficult to replicate, just costly.