[Mizza]

More importantly - why do innovations by NASA not go into the public domain?

Our tax dollars paid for it, our homemade battlebots should be armored by it.

[V_Terranova_Jr]

NASA does publish on much of its research. See, e.g.: https://ntrs.nasa.gov/

There are other forums in which they publish export-controlled information.

They patent things for at least two reasons. One is monetization - some in Government believe that monetization helps recoup some of the taxpayer's R&D contributions by claiming a "rightful" share of the benefits to commercial entities. I'm not saying I agree with this, just that is it a commonly held viewpoint.

Another, even in cases where the licensing is royalty-free, is for defensive purposes. It ensures a benevolent entity owns the patent and can license it for implementation in an equitable and non-discriminatory way.

Practically speaking, if you were to implement NASA-patented technology in a non-commercial context (homemade battlebot), it's extremely unlikely NASA would come after you for patent infringement.