I know a guy who did a website related project for NASA. Was all smooth sailing till he was just about done and needed a server to put it on. The massive bureaucracy kicked in and everything grinded to a halt. It ended up being hosted on some random server it wasn't really supposed to be on because that was the only thing that could work in a timely fashion.
Because that's the right way to leverage social media: Meet your audience in the places they exist, so they can use and share your content, natively. They also posted this to Twitter, and perhaps other platforms.
So they can focus on space exploration instead of web site maintenance?
I understand why they use YouTube for video hosting (video hosting is difficult and expensive) and have a prescence on social media (to reach a wider audience), but yeah, Tumblr is a bit strange.
NASA's online prescence is a bit fragmented in the first place, their different facilities have their own websites, social media accounts, etc.