They were banned because they don't decompose, so they end up all over the place. Not just in the ocean, but on the beach, in creeks, lakes, anywhere near a highway, etc. As an example local to Silicon Valley, Stevens Creek used to be completely clogged with plastic bags. It's gotten a lot better now.
Of course any wasteland or street is still littered with fast food plastic, plastic bottles and the excessive packaging found in most supermarkets.
We have slightly effective recycling schemes for a tiny proportion of what we use, and massive amounts of recycling end up shipped to the developing world to be dumped. Manufacturers of TVs, appliances, IoT toys and any thing else using plastics aren't required to own their debris at end of lifespan.
So, as is typical with modern politics, we've had a token gesture that affects the public but utterly avoids the real issue.
The oceans are doomed unless we grow up and own our debris as a species.