We've had 40 years of Chevron deference, during which time Congress wrote laws expecting that this is how they'd be interpreted. If they didn't want this behavior, they could have passed laws about it. Or included some boilerplate language within new laws about how the agency has to defer to courts for interpretation of those regulations.
(Granted, by the same logic, they could presumably start adding some "these rules should be interpreted according to the agency's definitions" boilerplate to new laws, if they really want that.)