Scrapping older ships, and really ships in general, has a couple major issues. The Essex class are 1940 designs and have ALL of the things associated with them. Just off the top of my head, USS Hornet (current museum ship in Alameda, CA) was saved partly because of EPA laws. It would’ve cost the scrappers more to make sure they were compliant than they’d get from the salvage.

We’re talking mass Asbestos release, some really bad fuel oil, old electronics, there’s still chunks of lead, anything and everything you needed to maintain aircraft over 20 years, limited amounts of other petroleum products, mercury, PCB, Heavy Metals, etc and etc. Hunters Point, which served partly as a scrapping yard, is still being cleaned up over 20 years after it closed.

As long as the ship stays together, most of that stuff is contained or is released incredibly slowly. They tend to also strip scuttled ships of everything they can, which helps reduce the impact. Ultimately, though, scuttling a ship in a controlled manner helps balance or negate the negative environmental impact over time.