There are many reasons. Union labor and excess government are often cited by libertarian writers. I think you can begin to unravel some of the problems by reading Environmental Protection: the Enemy of Green by Anthony J. Ciani over at the American Thinker. In Ciani's thinking, the issue is that we have become so good at measuring pollutants with modern spectroscopy, that it is possible to see pollution everywhere. People who discover harmful pollutants in their environment don't seem to ask the next question: is it harmful in the quantities found? Apples contain arsenic, but nobody has ever died as result of eating apples. But, as long as nobody knows about the arsenic, that is a naturally occurring substance, nobody is the least bit worried about it. Out of sight, out of mind.
Another issue comes as result of people not thinking through the entire process. All of the chemicals we commonly use are natural, and in the environment already. A case in point is cadmium, a toxic metal in high enough doses:
So what has a radical crusade against toxic metals gotten us? One company wrote a proposal to the Department of Energy to investigate a way to make cadmium telluride (CdTe) solar cells more efficient. Many of the reviewers thought it was a good idea, but one reviewer said, "nothing with cadmium is any good." The proposal was not funded, probably beaten out by a shrimp treadmill, but at least that reviewer prevented all of that cadmium getting from our environment back into our environment. You see, whether it is used to make solar cells or not, all of that cadmium comes as a byproduct of zinc smelting. It has to go somewhere.(The emphasis is mine. If it is possible to increase the efficiency of solar cells using cadmium telluride, it seems reasonable to at least explore it. I do not consider fossil fuels to be the great evil that some people do, but like them, I would like to be able to use less of them if I can do so economically. I am slowly relamping my own home with LED replacements, which cut energy use by a factor of 10. We'll see if the extra costs of these bulbs is outweighed by the longer life, and lower energy costs.)
The EPA has been run by zealots since it was founded. It needs to be run by more practical people who understand that a safe environment is only one of our values, not our one and only value. If our ability to make things and to innovate is crippled, to the point that no one has a job, it is little comfort that the food we can't afford to purchase, the home we can't afford to buy, the car we can't afford to drive is free of all environmental hazards.