The nationalist politics is an organic expression of the population. Croatia wasn't created by a nationalist coup d'etat but by a democratic vote. Two decades later it joined the EU, which is hardly the behavior of a nationalist fervor. It's a similar story for the other former republics.

By contrast, any claimed Yugoslavian identity is a function of a repressive (communist) state since its creation was by fiat. Croatian and other identities predate the creation of Yugoslavia but their expression was suppressed in the service of maintaining its existence. Tito is renowned for pulling this off but after his death things unravelled over time.