Oh it gets worse. This change is just the most recent in a series of states updating their laws since 2017. Because a study was released that showed almost 200,000 child marriages in the US between 2000 and 2015. And over the next three years years another ~100,000 happened.
And while it's important to remember that a 17 year old marrying an 18 year old is technically child marriage, and 16-17 year olds girls who marying men who were over 18 or older but less than 29 is over 90% of those statistics. There were dozens between girls who were 12-14 and men who were 40+, some were 60+. And that it is still legal in several states if certain criteria are met.
https://en.wikipedia.org/wiki/Child_marriage_in_the_United_States
The vast majority of American movie and tv just use 18 regardless, to avoid any legal issues
Which is why a lot of Americans, even ones living in states where it's 16, think it is 18 in all states.