There has been a change. The traditional supporters of reunification are outdated.
The original Irish nationalists would not want a weaker national identity but a stronger one through unification. I've heard that the older supporters feel that something has been compromised. I'm not saying older supporters are racist - rather that the ideals they have of an Irish people and nationhood are not being promoted by their previous political champions. The people hold outdated views. Newer adopted ideals of immigration and open borders are perceived to be more important than campaigning with these older ideals for reunification which many consider to be at odds with each other in some ways.
My impression is that their old views are comfortably dissolving away than being actively or angrily being fought for which leads to less enthusiasm about the issue. The notion of what Ireland is to them is less important now. They have more peace with a corresponding weakening of the Cause.
Many modern people today consider the very notion of national identity as outdated and troublesome. From Ukraine to Palestine, its based on the thorny issue of nation and people. The Troubles were based on the issue of nation and people.