I think what you're missing here is most OpenAI users aren't technical in the slightest. They have massive and growing adoption from the general public. The general public buy services, not roll their own for free, and they even prefer to buy service from the brand they know over getting cheaper service from somebody else.

The conclusion I got from their comment was that the highest margin tier (the business customers) would be incentivized to build their own service instead of paying the subscription. Of course, I am doubtful that for the vast majority of businesses this viable/at all more cost effective when a service AWS is highly popular and extremely profitable.