Because he was the most right-wing ideologically since FDR he had an aversion to any kind of government regulation, and the environment was one of the issues during his Presidency where his agenda was not supported by the majority of the American people, even many of his own voters. Conservatives place a higher value on industry's freedom to do what it wants over any kind of environmentalist demand. Whenever the environment is an issue, there is always a conflict between making money (and protecting jobs) and promoting environmental concerns. Most Republicans want clean air and water of course and they do care in general about making their surroundings clean and un-polluted. This is one of those issues where there seems to be a consensus but the industry (donor) apparatus of the Republican Party refuses to allow for the consensus to rule.
The general public has largely accepted some of the more mainstream environmentalism since the 1970s - and children in schools, at least since the 90s, have been taught over and over that the environment is worthy of protection. Even in apolitical schools in conservative small towns like mine, millennial kids were taught that the environment is a major concern. This was reinforced by popular movies and TV shows, class projects, extracurricular activities, and the media.
Reagan didn't have an aversion to any or all types of government intervention. He took umbrage with his critics characterizing him as wanting to undo the New Deal, for example. His issue was with the Great Society and those associated programs (which included the environmental regulations). Reagan was not a paleoconservative; he accepted Liberalism to a degree - up to and including the New Deal. He was vehemently against the New Frontier/Great Society though. One must remember Reagan spent more than half his life as a very left wing Democrat. This is a guy who campaigned for Helen Douglas against Richard Nixon, and Helen Douglas was considered even in 1948 to possibly be a closet Socialist - out of step with the mainstream left of the day. Those core tenets didn't wash away completely - he didn't switch parties until he was 51 years old - but he did hate the Great Society and I do not think he *understood* environmentalism.
