Because the left is looking for any reason to be outraged, as long as they don't have to do anything, and they can reject all the blame and anger towards another, preferably successful, group of persons :
"In reality, your straw usage has almost no impact on the ocean whatsoever. That’s partly because the “500 million straws a day statistic” is invented, and partly because the United States as a whole contributes very, very little to the plastic waste problem. About 60% of the plastic in the Ocean comes from five Asian countries: China, Indonesia, the Philippines, Vietnam, and Thailand. Indonesia’s Citarum River, the most polluted river on Earth, is essentially a massive trash heap on a giant aquatic conveyor belt. Every day, 20,000 tons of waste and 340,000 tons of wastewater are dumped into it and then ferried to the ocean. In places like Vietnam, plastic in the water is the least of anyone’s concerns. Raw sewage is discharged directly into water ways, turning the rivers toxic."
http://www.patheos.com/blogs/geneveith/2018/07/why-banning-straws-will-not-save-the-oceans/