Your specific example of your college boyfriend as someone who was lucky to grow up without faith is interesting, but some of what you observe is as much about the difference between Christians and Jews as it is about atheists and believers.
First, Jewish and Christian definitions of faith have always diverged. All you need to be a Christian is to believe. As I was always told growing up, even if you don’t believe in G!d at the moment, you should keep the rituals — because you might believe again someday, and because the study of Torah is said to lead to doing mitzvot (good acts, the opposite of sin), whether or not you Believe.
I’m no expert, but I’ve always thought that around the turn of the century there might have been more Jews who believed in a personal and interventionist G!d. One of the scars of this century is that it’s very difficult to believe in a power that would do… anything at all… if something worse than your worst nightmare came to pass. At the same time, many of our parents and grandparents tried assimilation, and it didn’t make them any less afraid (see also: almost everything about the state of Israel and the diaspora’s reactions to it). The other millennial Jews I know see assimilation as just another kind of death and disappearance.