I'm guessing those marriages are likely correlated with strong shared religious beliefs[1] and closeness to extended families that help share the burden of raising children.
That’s definitely not true in my circle of friends. Of my 6 closest high school friends (all female), the ones who didn’t date in high school all married first, to either their first or second partners. The ones who dated a ton are still dating in their early 30s. None of us are very religious, and we all live in traditional (American) families with commensurate amounts of support.
Negative selection bias as in people who are less capable to maintain long term relationships are more likely to have a lot of dating history.
Conversely, people who are super easy going and great partners to be with may have very few people break up with them (and kind of succeed on the first try).
Or another way to put it: To have a long dating history with a lot of different partners, you need to have broken up (or been broken up with) quite a few times. This could be due to circumstances outside of your control, but that is probably not true for all people in that category.