Pretty much this. Besides, what target would Putin have at this point? To target anywhere in Ukraine, would be to poison the whole endeavour, he needs to take Ukraine in one piece - and effect regime change in one fell swoop. The prize is gone, if you inherit a country you've destroyed. Hit anywhere else, and NATO will respond.
He's dedicated and committed, or has placed within striking position, by most estimates, up to 60% of Russian conventional forces within striking distance of Ukraine.
Now, let's just think about for a second. Many military analysts would have thought that mobilising 60% of conventional Russian forces would have not only seized all the Baltics and most of Eastern Europe within 48-72 hours (Admittedly, I don't know if that includes calling up all reservists - which to my limited knowledge, he has not). Now, granted, they haven't fully committed all their forces yet, but most estimates would've said that in 72 hours the Russians would have taken not only taken Lithuania, Estonia, Latvia - and would be rolling through and bearing down on Warsaw, Budapest and Bucharest by now - Ukraine would have been an afterthought. They haven't even taken Ukraine, so far, which was considered basically a highway to larger action. That's before we consider that not a single NATO shot has been fired. Let's be fair, this isn't WW3 and Putin so far isn't launching a full-on assault on the NATO countries but still, think about it. Many analysts would have thought within 72 hours - it's NATO that would have had to deploy tactical nukes contain the Russian advance - not the other way around. This doesn't even take into account that the Russian eastern flank would be weakened and exposed. They could end up not worrying about Russian speakers Ukraine, but having Moscovites and Siberians learning how to speaking Chinese.
My point, this is not going well for Putin. Not at all.