Training those models are extremely expensive and it's gonna find a way to recover that cost through one way or another...
The issue here isn't the cost to run the service, it's the name.
An analogy would be a restaurant called "free lunch" that charged money for lunch because food supplies are expensive.
I thought the model was publicly shown? You can take that and do your own training and make your own API, right?
No. GPT-2 is available to the public, at least up to so many millions of parameters. GPT-3 has so far been released exclusively to a small number of beta testers with strict rules on what you can do with it.