But it’s not a power grab at all. Nations apply to join NATO of their own free will. They’re not forced at the barrel of a gun.
These former Soviet block countries made their own choices
Those nations are not the people. The leaders of those countries make a choice that being inside NATO will assure them of being part of a geo-political order that's attempting to secure more of the world's material resources and they back them to achieve it over Russia / China and want protection too.
Look at the grief those BRIC national leaders get for not jumping to it and backing NATO's stance in Ukraine. They havent done it because they want to leave themselves open to triangulate and get the best outcome for their international group...they get to do that because they're so economically powerful and cant be cajoled by the west to throw in with them and come under their miltary umbrella....that's not the case with those nations who've fallen into line since 1999.
In short: there's a compulsion here. Those national elites in northern and eastern Europe feel the pull of NATO, yes. But they also cant really do anything other than fall in with the growing bloc.