While I agree with your reasoning about the driving factors for the Eastern Europeans to join NATO, I think a bigger question is not why they wanted to join but why they were allowed (and encouraged) by NATO to do so. One can argue that accommodating the fears of the former Warsaw Pact states while antagonizing Russia by doing so, to put it mildly, showed lack of foresight. The sole purpose/target of the organization's existence was given every reason to be weary and fearful of the organization. A possible alternative could have been to actually mean what they proclaimed by "partnership for peace" and try to forge that peaceful partnership with Russia - where the mood toward the West at the time was far different from what it is today, unfortunately. People were very hopeful that the cold war was left behind and were looking forward to a much friendlier relationship with the West. That evaporated in the 90s, thanks to the NATO enlargement, to a significant extent.I have explained why I believe several of the ex-Warsaw Pact nations joined NATO, some a decade after becoming 'independent' of Moscow. Naturally, I have a potentially different perspective from others which colours my thinking.
Are we going to get an alternate explanation for why countries like Poland joined NATO?