Actually there are two dominant sources of micro plastics in the oceans: tires and asphalt. There are other sources as well but those are the big ones.
If you think about it, roads need regular up keep because they erode away. Same for tires, which need replacing regularly. Where does that material go? Well it all gets ground into small particles as cars and trucks use the roads. Car tires get warm when you use them because of friction. That friction inevitably wears out the roads and the tires. So you end up with fine dust and particles that eventually washes away when it rains and ends up in rivers and eventually our oceans.
So, converting plastic bags to asphalt is a great way of ensuring a lot of it ends up in our oceans.
The challenge with plastics is not necessarily recycling them but figuring out what is what so you can recycle them properly. Household trash is full of a wide variety of plastics. Sorting these and processing them is not impossible but a bit of a challenge if it's all mixed up.
There are some startups innovating in this space and it's not completely hopeless at this point. Also there are new materials that degrade better/more predictably, certain bacteria have been discovered that actually eat plastics, and we're figuring out cleaner ways of producing source materials in ways that don't involve using fossil oil.
But maybe converting oil to plastics for 1 use products or packaging should just not be that cheap as it is currently. The attitude of "it's not our problem" for both producers and consumers is the core issue. Make it their problem and it's suddenly a lot less attractive to use plastic because cost goes up when you do that.