There are risks associated with releasing historical proprietary models that were not designed for open release:

- It is trivial to extract samples of the training data that was used, which can bolster existing lawsuits/foster new ones.

- Older models are not as safety-hardened, so it is easier to coax unsafe behaviour out of them, which is a PR risk.

- It may be possible to divulge proprietary secrets from the model (e.g. architectural details that may still be relevant).

For these reasons, and more, it's unlikely that GPT-3/similar models will be released until these concerns are no longer relevant (e.g. when they become a purely historic concern, similar to the open-sourcing of other proprietary software from decades ago).