Because knowledge and early warning systems might erode someone's profit margins:
AMBIENT AIR MONITORING
SECTION 4.25.(a) The Department of Environment and Natural Resources shall review its ambient air monitoring network and, in the next annual monitoring network plan submitted to the United States Environmental Protection Agency, shall request the removal of any ambient air monitors not required by applicable federal laws and regulations.
SECTION 4.25.(b) No later than September 1, 2016, the Department of Environment and Natural Resources shall discontinue all ambient air monitors not required by applicable federal laws and regulations if approval from the United States Environmental Protection Agency is not required for the discontinuance.
SECTION 4.25.(c) Nothing in this section is intended to prevent the Department from installing temporary ambient air monitors as part of an investigation of a suspected violation of air quality rules, standards, or limitations or in response to an emergency situation causing an imminent danger to human health and safety.
Of course, it never crosses their mind that keeping (a) & (b) in place would very possibly prevent (c) from ever happening. The GOP is likely working from the hypothesis, "If the air gets bad enough, we'll know because birds will start falling from the sky and people will be getting nosebleeds." Idiots.