No one ever comments about the pollution caused by WWII. Dozens if not hundreds of oil tankers were sunk from New Guinea to the English channel. Carriers went down. Planes went down. Every nasty chemical you can name was strewn across the planet. Two A-bombs were dropped. Yet things looked pretty good not that long after. Who cleaned it all up?
Presumably the people living nearby. Quite a bit of it isn't cleaned up; I've been to an atoll in the Pacific that I have to leave unnamed where you can still see rusting landing craft offshore.
As for oil, when it spills, the volatile component evaporates and the heavy component (tar) eventually sinks. If it sinks into the deep ocean, like every other organic material it'll eventually get broken down by bacteria. But that takes time.
I lived in Valdez for 18 years.
My husband worked up there every summer until 1992. He was there for the oil spill "cleanup." It was a money-maker for EVERYBODY. The big winners, of course, were the enviro-wackos, who cleaned up on Exxon. The locals were charging $250 a night for a bed in a mobile home, more if the house was stickbuilt. The fishermen didn't fish the salmon run that year because they could make $1000 a day renting out their boats to the cleaning crews.
The steam cleanup on the beaches did terrible damage to the beaches by killing all the normal bacteria (including oil-eating microbes) and sterilizing the gravel.
The cleanup of the mammals was NOT, shall we say, "cost-effective?" It cost around $35,000 to clean up and rehabilitate one sea otter. When the big day came to release little Oscar back into the ocean, the schools sent the students to the beach to watch the release. Oscar was released from his cage, and cheerily swam out about 250 feet, where he was promptly swallowed by a killer whale.
The oil was a form of asphalt, the same stuff that companies use to line their water tanks and seal them from rust and leakage. When this stuff gets cold, it hardens and becomes inert.
One smaller enviro group went, with a lot of publicity, to "rescue" some seals and fish that had gotten "trapped" behind a glacial dam which formed a "dumping lake." They made a lot of noise, took a lot of pictures and money from sympathetic dupes, and watched stupidly as the seals casually climbed over the ice dam and swam out to sea. The trapped salmon were caught by these enterprising enviros, and they had themselves a nice little salmon roast by the side of the little lake, which, incidentally, dumped about two weeks later.