You don't have to teach anything. If someone has a better place to throw their trash than their local dump pile, they'll do it because they don't like that place either. The vast majority of river plastic comes from developing counties with poor trash infrastructure. Plastic pollution is largely a solved problem. There may be plenty of assholes who leave their garbage on the beach in the US, but when they're home, their waste still gets properly disposed of.
It makes sense to prioritize tackling low hanging fruit with solutions that we know to work rather than ones that inconvenience us and make us feel like we're doing something, but don't actually do anything. The only benefit the LA Times article mentions is that there are fewer plastic bags found on beaches, but since "reusable" grocery bags are significantly heavier than the old disposable ones, I'm not convinced it's actually any better in that aspect as well.
The LA Times' findings just take us full circle back to my original point. I thought keeping plastic bags off our beaches (and other environments) was supposed to be the primary benefit of the ban.
One heavy plastic bag may look visually less offensive than 3 lighter ones, but is it better for the environment? Would the money people spend on "reusable" disposable bags be better spent on enforcement of littering of cleanup?
https://theoceancleanup.com/sources/