AlphaGo and AlphaZero are Google/Deepmind, not OpenAI. They've released papers, and there's a model that reproduces the paper.
While they released papers, I personally wouldn't have been happy reviewing the paper, because it was basically impossible for anyone to check (given how long Leela Zero took to get up to the same level). Releasing the network via bittorrent would have been very low cost.
I am impressed by Leela Zero, and independant duplication is still important, but it would have been even better to be able to directly compare it to AlphaZero & AlphaGo, rather than having them locked up.