These ships were abandoned over twenty years ago. Their owners left them to die after the Chernobyl disaster due to their high levels of radiation. One of the great ironies of the this particular tragedy is that many animals and trees are now doing considerably better in the Chernobyl region, than when the humans were there. General principle: When next nature fails, old nature makes its revival.
Via. See also: Where ships go to Die, Man made Sun.