“Why has NATO Expansion has increased since the fall of the Soviet Union?”
Because former Russian satellites know what it was like living under the Russian boot, and do not want to live through it again. And they don’t trust Russia. So, they joined NATO for protection.
Using your NATO expansion argument, the Luhansk, Kherson, Donetsk and Zaporizhzhia regions are holding safe and secure elections to join Russia for protection from NATO, Washington and London.