The price of a cluster similar to the one OpenAI used is orders of magnitude higher. We are talking about a price tag that at the very minimum would be in the 150M+ range, you can probably multiply that price by 2 or 3 (10 thousand V100, 300k CPUs, infiniband between every node, network storage etc.).

Almost no one has that kind of money to invest up front (especially not an hypothetical open source organization like discussed here). Even if somehow one had that money available, for this to be more economic than renting you need to have it running at full capacity at all times for years, not many research groups can come up with many interesting projects at a scale large enough to utilize that kind of cluster efficiently.

So buying something like that is only conceivable for huge research groups with hundreds of researchers and tons of cash: Google Brain, DeepMind, Microsoft and probably Facebook. Even OpenAI wasn't able to afford it directly...