It's a garbage article. The actual data is noisy AF. Here it is thrown in Google Sheets real quick:
Fuckin' ALL THE SEX is going down, man! What's going on?
It appears that "fuck your survey" is the most common sexual frequency. It's still noisy, but predominant.
But I mean, shit. The total number of respondents isn't governed at all. They vary between 1500 and 3000 people. What if we crack that down to percentages?
Yeah. Amount of sex reported goes down every year that "fuck your survey" goes up.
This is bad science.