Crossroads is set in the '70s, but is only lightly sprinkled with period references. Almost all the diction would fit into any of Franzen's worlds.
The characters largely sit around wondering whether they're good people; what their badness consists in, if they're bad; and how to find God. This is Franzen as an American Dostoevsky. (Certainly this stuff isn't what ties the novel specifically to the '70s.)
The manifestations of those topics, though--good, evil, self-doubt, God--involve: relevations about "social justice" (a phrase that appears three times) and the systematic mistreatment of women by men and of non-whites by whites.
Those issues are politicized in the Callard sense: "action and speech in that area must be interpreted against the backdrop of some standing debate." A 2022 reader could not read a book set in or around 2022 without immediately interpreting a remark like, e.g., "the Crossroads-encouraged inflation of emotional scrapes into ambulance-worthy traumas" in light of contemporary debates.
Here are two things that distinguish fiction from other forms of communication: First, there's a presumption that things happen for reasons. Those politicized subjects are presumably necessary in Franzen's project. Second, one's raw aesthetic reactions matter more than they do in other contexts. There are settings where we can say "I know this is politicized, but let's try to just talk about X here." A novel is usually not one of them.
But part of what produces that raw aesthetic reaction--that is, the reaction we have when we see a politicized topic and interpret it against the backdrop of a standing debate--is our understanding of the world in which the topic is being presented. So by setting the book in the '70s, Franzen opens up some of distance between those topics and our current debates.
Yet those topics remain thoroughly politicized for us, despite being less or differently politized in the world of the book. It's only some distance that gets opened up. How much distance that is depends on many things, surely including the reader.
The novel exhibits Franzen's full awareness that these issues are politicized and that some episodes in the book, in which characters do things that are presumptively OK in the world of the book, are only that way because the novel is set fifty years ago. In a climactic scene, someone says something like: "This is OK; it's the seventies." It's hard for the reader not to feel called upon at that moment to compare our world to the novel's.
I suspect it's wrong to read Franzen either as longing for a world where the old norms applied or as creating distance between our world and the novel's only to give us a perch from which to feel superior. For me, at least, there was room for a fresh and valuable look at various human depravities and struggles...
...including the struggles of religious faith, which are different for the characters (as opposed to us) because they're living in a more religious world.