I legit don’t get how come there isn’t some government funded publication platform. No other endeavor has as much bang for buck. Arxiv needs $2.5m a year https://arxiv.org/about/reports-financials which is chump change.
On the other hand, PubMed exists.
My guess is, for a preprint archive, network effects are paramount, and ArXiv was there first. It’s not directly a government project, but is still funded by US government grants and hosted by Stanford (now that the international mirror network is shut down, which does give me a slightly jittery feeling).
[1] https://hal.archives-ouvertes.fr/
[2] https://groups.google.com/g/isl-development/c/JGaMo2VUu_8