From the article:
"When it comes to sexlessness (“no sex in the last year”) among young adults, the biggest change comes post-2010."
"Between 2010 and 2019, the average time young adults spent with friends in a given week fell by nearly 50%, from 12.8 hours to just 6.5 hours."
No doubt there are other factors too, and all of the factors are entangled together as in any complex system, but I think internet and smartphones is one of the biggest aspects to point to.