I'm not too informed about the South Korea market specifically either, but reading about it, what the news suggest is that the decrease in DUIs in SK are heavily correlated to progressively stricter DUI laws over the years.

I'm not sure to what extent we can infer a correlation between the app-based aspect and DUIs there.

Though to be clear, I do think the app-based aspect plays a role. It's just that when I say "rideshare", I assume we are talking about the whole package as it exists in reality, as opposed to dissecting what aspects of Uber affect what types of statistics.