Seriously Striking Moscow (for example) would almost certainly result in a swift, all out retaliation from Russia towards Ukraine.
A large portion of the Russian military has been held in reserve for defense, on the grounds that a full NATO invasion could decapitate the regime (a la Iraq in 2003).
Lemmyites are convinced the Russian military is entirely exhausted and these suicide incursions represent territory Ukrainians can actually hold. But there’s much more of a long game at play, as Europe and Russia wage a proxy was of attrition across Central Europe, Central Africa, and the Middle East.