You seem to be assuming that countries may decide on their own freely who they associate with. This is the case in international law, but not in reality, as can

You seem to be assuming that countries may decide on their own freely who they associate with. This is the case in international law, but not in reality, as can be seen in many examples concerning Russia or the US or China. Realpolitik vs ideal-oriented policy. It wasn’t the buffer states driving the decision, it was the US and NATO. They had to choose between buffer states and expanding NATO. The developments in Ukraine were predictable and likely avoidable had they chosen differently - see the fate of Belarus or Georgia or Ukraine before 2004 and before 2014.