They don't release that information because they don't want to lose their competitive advantage to other companies. It's a race towards AGI/Transformative AI. It could alsoo be a race for resources: e.g. convincing the US government to concentrate its funding on the leading AI project alone. This means any release of details may come only when OpenAI knows that trainnig for the next generation of models is running without problems.

This is likely based on the idea that newer models can be used to design/build/train the next generation of models, leading to an exponential amplification of capabilities over time that makes any lead time over the competition a decisive factor.