They saw chevron as useful when Republicans had control over all the major agencies, but with gov agencies driven by experts and scientists who can ignore the Republicans screaming then chevron isn’t helping them anymore. And that’s part of why they try to get as many partisan judges into the system as possible, to get their way through corrupt courts instead.
With Chevron, it would stand, without it the court gets to ignore all reason and reject an agency’s interpretation even if it’s sane and carefully constructed by experts. The court gets to challenge every individual decision and reason made by the agency which the law doesn’t make explicit