Reverse roles for a moment as assume red and blue swap colours on a map. Since 1989 who's been more expansionist? If the USA was in Russia's position and saw a former neighbouring satellite leaning towards a new allegiance to the old enemy do you really think the USA would have been so patient?
I'm no apologist for Russia, but they've clearly concluded Ukraine is a bridge too far after lesser allies have already switched.
Where I think the US/NATO/EU has been short-sighted, and I wondered this in early days when there was heretical talk of former WARPAC countries joining NATO, is surely increased membership de-stabilises both the unity and strength of the alliance and increases the likelihood of conflict as there are more moving parts likely to clash? So why dillute?
Take that one step further and look where these countries are in relation to the opposing superpower - let alone taking into account their resources and strategic importance (Sebastapol) - and why on earth are we surprised that Russia has done anything less than they have?