I dont think thats the cause directly.

I think on the whole a book called "Bowling Alone: The Collapse and Revival of American Community" which was published in 2000 that expanded on a 1995 essay of the same name predicted this.

Mainly even before the internet was good there was already a sharp decline in community involvement in things such as labor unions, religious groups, parent-teacher associations, women's clubs, military veterans organizations, boy scouts, fraternal organizations, etc.

The internet just accelerated this trend.

My conjecture is that younger millennials and gen-z are an internet first generation and lack some of the social skills and social circles that lead to relationships. The average high schooler and college student has way less sex than in previous decades and these groups aren't really basing their sexuality on economics.

But I'd imagine beyond just the social changes, that the economic situation of millennials and gen-z impact things as well.