The issue here for OpenAI is that they can limit what their harness can execute, but if they try to sell API access to the model, someone else would try to rebuild that harness, and in all likelihood be able to succeed pretty well (especially once they get things running to the point of being able to use the model's reasoning to help them come up with clever obfuscation and such).

They are a company that's built a business and crazy-high valuation on "this is 'intelligence' that we can sell to everyone as a service" but seem to have ended up instead in the much-smaller-addressable-market space of "this is a weapon that we can't sell to just any old person off the street."