No, it's an actual concern...lots of left-leaning folks in the my family.
And for a few of them that are on the younger side, Anti-Trumpism & getting on board with every left-leaning activist movement has been the nucleus of their social life for the majority of their adults lives. I'd prefer if they didn't end up depressed and aimless when "there's no more Trump to hate".
There is research to suggest that those types of relationships and social circles may not be as durable.
Per Psychology Today
If activism becomes isolated from other life-spheres or if an individual’s broader life changes (such as shifting priorities or identities), these relationships may be more vulnerable to dissolution compared to friendships built around a wider range of shared interests. In contrast, relationships grounded in shared interests—such as hobbies, sports, or professions—often benefit from the flexibility and variety of contexts in which those interests are pursued, potentially making such friendships more adaptable to life changes
There is also the phenomenon of what they call "reverse culture shock"... one of the common examples of that is "Post Burning Man Syndrome" (or as some call it "Post Playa Depression"
Where after a person immerses themselves so deeply (and myopically) in one particular ideological environment, there are coping issues when that finally ends.
I can see this being a longer-term version of that. If a person's social life and "friendships" has been entirely wrapped up in "opposing Trump", what happens when that common thread disappears?
Durkheim's theory of "collective effervescence" could explain some of it. That theory was originally applied to understanding peoples' connections to religion, but I could just as easily apply here.
Where if a person's entire social life is wrapped in that church social circle, that "sense of belonging to something" becomes more important than the stated reason for being there.
How that would apply to this situation, if a person felt a "feeling of belonging" by participating in some form of social activism, joining additional movements could be less about the new issue itself, and merely more about "getting that feeling back", and why we see the immediate "okay, now we need to elevate it to the next thing"