It’s a very substantial aspect of “being poor is expensive”. Polluted places, and the sorts of places where pollution tends to collect, are undesirable and thus cheap. The rich historically buy the high land and thus are not affected as directly by flooding, which these days also comes with a dose of pollution.
Ironically all of the rich people migrating to waterfront property may be what finally gets us past where we are today with waterway pollution and global warming.