A law passed by a legislature is rarely the document that regulated parties actually follow. The operative text is usually a rule written afterwards by an agency, and producing it routinely takes years.
The statute delegates rather than specifies
Legislation often sets an objective and leaves the technical content to an agency. A statute may require that emissions be reduced without saying which measurement method counts.
That gap is deliberate. Legislators lack the technical staff to write engineering thresholds, and a specification frozen into law would be hard to update as methods improve.
The consequence is that the real decisions move to the agency, where a separate procedure governs how they must be made and documented.
Notice and comment is a genuine burden
Most systems require an agency to publish a draft rule and invite public comment before finalising it. Anyone may respond, and large rules attract enormous volumes of submissions.
The agency cannot simply file those away. It generally has to show that it considered significant objections and explain why it accepted or rejected each line of argument.
Reading, sorting and answering comments is the single largest time sink in the process, and it scales with how contested the subject is.
Analysis requirements run alongside drafting
Rules of any consequence usually trigger mandatory assessments: cost estimates, effects on small businesses, paperwork burdens, and sometimes environmental or federalism reviews.
Each assessment has its own methodology and its own reviewers, and a weak one can send the draft back for rework long before the public sees it.
Legal exposure sets the drafting pace
Finished rules are frequently challenged in court, and the usual ground is procedural rather than substantive. A challenger argues the agency ignored evidence or exceeded its statutory authority.
Agencies therefore write defensively, building a record that shows every step was reasoned. That record is the main defence available if the rule is contested later.
Careful drafting is slower, but a rule struck down after four years costs more time than one that took an extra year to write properly.
Publication is not the end of the clock
A final rule normally carries a compliance date months or years ahead, giving affected parties time to adjust systems, retrain staff and buy equipment.
Meanwhile a new administration can begin the process of amending or repealing it, and doing so generally requires repeating the same notice-and-comment steps in reverse.
Reversal is therefore slow in both directions, which is why regulatory change tends to lag political change by a considerable margin.