NASA has always carefully crafted and maintained their image as totally competent and science-based. While UFOlogy is a genuine study, it also has a well-known crackpot factor, and NASA doesn't want to be touched by that in even the slightest way.

Ufos made illuminati.

Ufos hide illuminati.

Let's do this! (probably won't happen tho)

The whole keeping it a secret crap is what's so annoying. I have found few instances where the "secret" they keep is really that valuable. lol