From the summary for Counting Regulations: An Overview of Rulemaking, Types of Federal Regulations, and Pages in the Federal Register (R43056, Updated September 3, 2019):
Federal rulemaking is an important mechanism through which the federal government implements policy. Federal agencies issue regulations pursuant to statutory authority granted by Congress. Therefore, Congress may have an interest in performing oversight of those regulations, and measuring federal regulatory activity can be one way for Congress to conduct that oversight. The number of federal rules issued annually and the total number of pages in the Federal Register are often referred to as measures of the total federal regulatory burden.