I'm guessing there's lots of Apis from the wayback that are URL dependent and diverting just web through all that madness over to the www servers isn't a cakewalk.
Maybe they do have some reason why it would be difficult to add a CNAME, maybe not.
> Setting up our infrastructure to do that is technically straightforward: we need to add more servers to handle a lot of additional traffic on the front end, before people get to content.
as a description of the problem, the above seems kind of nonsensical. Which suggests that even this blogger is in fact, guessing, and then worse just passing it off as an explanation, and then we're back to NASA looking kind of bad here.
Based off the wording, it sounds like they're responding to "why can't I browse http://nasa.gov/x without the www?" rather than "why doesn't http://nasa.gov/x take me to the NASA website?", but as they're a government agency, it's quite possible that there's so much bureaucracy / cost involved that it legitimately isn't even worth it to add a url-redirect server somewhere.