We also do it to preserve our unique prestine environment providing higher-order evolution. And we do it to preserve our ideas, our discoveries and our memories.
Then again, perhaps all worlds that develop truly high-order species require an quick evolutionary step wherein weird little monkeys fill the biosphere with plastic and get it suitably hot enough to being said high-order evolution. A period future historians will refer to as "the plasticene"?
I love that train of thought. Could be the basis for a sci-fi book.