There is only one security guarantor in NATO that truly matters. It is the US. You include a country into a security alliance only "If you are sure about defending it".. NATO is America's empire in Europe.At the time, Russia was crippled, so US thought that it could include Baltic countries ( which are indefensible against a Russian attack.. see suwalki gap dilemma) without a cost..Just like Ukraine now, the Baltic states and other Eastern European countries that Stalin forcibly absorbed after WW2 rushed to join the EU and NATO as soon as they we're freed from Soviet/Russian hold.
There is NO COUNTRY among Eastern and Baltic states would like to fall under Russia's sphere of influence - None!
... Except Lulashenko.
And because Russia is much stronger now, that is why inspite of all the noise, US has not included Georgia and Ukraine in NATO, because after 2008, US knows that US cannot defend them, and the days of cost free NATO expansion are over..