It isn't? AFAIK the whole decision making apparatus of the military and intelligence services are all there, neatly tucked between civilian stuff like museum etc..
And even if not, that seems just inflammatory and way more easily harnessed for huge propaganda wins for Putin & co, as opposed to suffocating like hitting refineries, airfields or other similarly painful and impactful but also further-from-the-everyday-people’s-minds-and-eyes targets.
if putin would be in the kremlin during the attack, he wouldn't be able to use it for propaganda ☠ but I doubt he's in there often. probably hiding most of the time, then do a few surprise appearances so he can't get ambushed.