Comment by CMay

After the USSR fell, they left behind many countries abused by Russia that didn't believe it would leave them alone. Those countries wanted defense guarantees in case of future Russian aggression.

NATO wanted to be deliberate and slow about admitting any new members, but countries that wanted to join felt that anyone who didn't join might get attacked or face hybrid measures from Russia to prevent them from joining next. So they grouped up and 7 countries joined NATO simultaneously. NATO was never begging them to join, they wanted to join NATO.

People push this vision of NATO being some hungry bastard that can't get enough, but it's largely outside pressures pushing countries to want to join it.

Sure enough they were right. Russia invaded both Georgia and Ukraine, which wanted to join already because Russia kept interfering in their societies.