[contrarian1234]

Is it? It's definitely not made immediately clear on their website: https://www.apolloremastered.com/the-project

Why are they on flickr and not NASA.gov as usual?

[gmiller123456]

In the US, government organizations are not allowed to copyright their work. They can, however, obtain works that were copyrighted by someone else. But pretty much everything coming out of NASA is public domain, though they don't put a lot of effort into publicising that fact.

https://www.copyrightlaws.com/copyright-laws-in-u-s-governme...

[porphyra]

Not sure, but I checked the licenses of a couple of photos on flickr and they were public domain.