This is a VERY interesting thread. I would say first and foremost it’s an economic issue. Our close friends have 5 kids and were living in a disgusting cramped apartment. They said “enough is enough” and moved to a much nicer home in Lakewood.
But Brooklyn is just part of a bigger picture. It’s just harder in America than a few decades ago. Israel will be increasing attractive to people. Unless you have a top-notch career here, it’ll make less and less sense to stay here. I’m not saying that America Jewry will collapse tomorrow. But we are definitely in the process of decline.
It’s part of our history. Do any Jews live in Pumbedita? Toledo? Lublin?