As someone who lives on the beach and lived on the beach since before these bans, plastic bags never seemed much of an issue and the real issue is that most people who visit the beach think nothing of leaving their garbage on the beach. Before the ban people tended to leave their garbage nicely contained in a plastic bag, now everyone just leaves it strewn about because they don't want to put garbage in their reusable bags that they use for their groceries which also would mean they would have to deal with the garbage instead of "forgetting" their plastic bag of garbage. The worst is the massive increase in sodden diapers, no one has a disposable bag for the diapers so they just leave them on the beach.
The garbage bags and plastic bag that wash up on the beach are insignificant compared to the garbage beach goers leave on the beach and people who don't live on the beach don't realize how much garbage that is because those of us who do live on the beach spoil our morning stroll and swim with picking up the garbage so the beach can be clean and ready to be spoiled all over again.