These countries were de facto already part of NATO, because they took part in all NATO exercises and all NATO military operations. Moreover, Ukraine has a special significance for Russia as the cradle of the Russian world.
Discussion
So, that means North Korea, China, and Belarus are basically Russian? They also take part in joint exercises.
Joint exercises don't give you Article 5. That's the trophy.
Finland was also part of the Russian Empire, but Ukraine is probably snazzier, I agree. And they wanted the Black Sea ports.
Russia and Belarus are part of a strange state that few people know about https://en.wikipedia.org/wiki/Union_State