Because the Great Pacific Garbage Patch really exists.
https://en.m.wikipedia.org/wiki/Great_Pacific_garbage_patch
The patch is characterized by exceptionally high relative concentrations of pelagic plastics, chemical sludge and other debris that have been trapped by the currents of the North Pacific Gyre.[2] Because of its large area, it is of very low density (4 particles per cubic meter), and therefore not visible from satellite photography, nor even necessarily to casual boaters or divers in the area. It consists primarily of a small increase in suspended, often microscopic, particles in the upper water column.
Research has shown that this plastic marine debris affects at least 267 species worldwide
Also, overfishing is real. Colony collapse disorder is real and affects wild bees. Monarch butterflies and others are becoming extinct. So are tigers and many other species. (although the trend has been halted for tigers).
The human population explosion and energy use explosion that grew even faster are the problem. Regardless of how efficient we get, we can't sustain such population growth indefintely. And Capitalism is extremely efficient at exacerbating negative externalities - whether factory farms, private prisons, weapons manufacturers or manufacturers of anything (plastic etc.) the incentive is to exploit negative externalities as much as possible to have more customers pay more money faster. The collective effect is perpetually increasing money velocity and increased velocity of exploiting externalities.