In the greatest generation, silent generation, boomers and gen X, the rates of obesity in teens and 20-somethings was a rounding error. People varied in attractiveness, but almost everyone would have been "dateable". Today, 20-30% of the young population is obese, which is going to severely restrict the dating prospects as well as throw off some of the youthful lust-based pairings that grow into relationships.
The overall statistics and various causes are interesting, but I wish the article had further broken down how each factor impacted things, eg, how much does income, education, bmi, male-friends, etc skew the statistics on romantic relationships.