As brutal as it might seem, plastic pollution is not a high priority. It makes for some shocking and upsetting photos, but it's not a fundamental threat to the marine ecosystem. The sources of marine plastic pollution are non-obvious and can be mostly mitigated through better management of waste rather than elimination at source.

Ocean acidification due to rising CO2 levels is a cataclysmic threat to the marine ecosystem. A relatively small decrease in pH could lead to the extinction of many key invertebrate species and the complete collapse of some habitats.

https://en.wikipedia.org/wiki/Ocean_acidification

The health risks posed by plastics are marginal at worst. There are some legitimate concerns about certain persistent organic pollutants, but plastics are not the primary sources of exposure to these compounds and their use is largely under effective control.