Of course, there are other reasons, but this is probably the biggest one. It is nicely summed up in two paragraphs in the article Whirlpools and Turbulent Flows by Geoff Olson in the September/October issue of Adbusters:
David Suzuki is another skeptic and he offers a great anecdote about economic thinking. While at the University of British Columbia, Suzuki figured it would be a good idea to supplement his academic background in biology with an understanding of economics. During the first class, Suzuki’s instructor stood at the blackboard drawing lines in chalk to show the flow from the resource base into the market, with subsidiary industries adding value and creating wealth for investors.
Suzuki pointed to the side of the blackboard that was empty of equations, the resource base, and asked whether the calculations took into account the effect of human activity on the environment, the diminishing reserves and growing waste that Suzuki reasonably regarded as a cost mortgaged into the future. “That’s an externality,” the instructor responded drily. In other words, the environment is something external to the grand human workings of the market and not worth factoring in. Suzuki left the class on the spot.
This post has not been revised since publication.