I am not sure what you are reading but those decreases are not trivial.

" Between 2009 and 2018, the proportion of adolescents reporting no sexual activity, either alone or with partners, rose from 28.8 percent to 44.2 percent among young men and from 49.5 percent in 2009 to 74 percent among young women. The researchers obtained the self-reported information from the National Survey of Sexual Health and Behavior and used responses from 4,155 people in 2009 and 4,547 people in 2018. These respondents to the confidential survey ranged in age from 14 to 49 years.