Because small countries of Europe that don't want to be invaded by Russia seek to join the alliance that was specifically created to prevent such eventuality for its members.
That's why of the 4 wars it has taken part in in the last 30 years, 4 have been wars of aggression while 0 have been defensive (article 5 was invoked for 9/11 but occupying afghanistan wasnt a defensive move it was an imperial move).
It's a dog eat dog world out there for sure but sometimes the 14 year old boy isnt safer joining the crips for protection from the bloods. Sometimes he's just sacrificed as a pawn in a wider turf war as the crips' promises of protection ring hollow.