Meta has released the model weights for OPT-175B, which is used in the paper. There's also a lot of full release LLMs from other labs on the way as well.
And on top of that, there are some questions on the quality of open source data (The Pile) vs OpenAI’s proprietary dataset, which they seem to have spent a lot of effort cleaning. So: open source models are probably data-constrained, in both quantity and quality.