They are using the “dating” apps to hook up. They don’t believe in the concept of family, marriage, or anything traditional, so why date in the first place? Life is all about getting your rocks off and posting photos on Instagram.
That's EXACTLY it. But it didn't start with Millennials. There are large contingents of Baby Boomers who have never married, or have married but never had children, or perhaps had one child.
I myself have always valued family and marriage, and in my senior year of high school met a like-minded young woman. We're still together and are enjoying plenty of grandchildren.
I share that only to point out that it is possible to live a traditional life if two people are serious about it.