In the early days of the United States, the 1st Congress proposed an amendment known as "Article the First," which aimed to establish a fixed ratio of people to Representatives. Although it was not ratified due to a flaw in its formulation, Congress continued to expand the House of Representatives after each census until 1920.

However, following the 1920 Census, Congress passed the Permanent Apportionment Act of 1929, which capped the number of Representatives at 435—a figure set back in 1911. Since then, major societal shifts have transformed the political landscape: the enfranchisement of women, Native Americans, and Black Southerners, and a tripling of the population. Yet, Congress has failed to adjust the size of the House accordingly. This neglect has significantly diluted the American people's influence over their federal government and has resulted in Congress delegating much of its legislative power to an expansive administrative state, often called the "4th branch of government."

Capping the house at 435 ensured that the power would continue to concentrate in relatively fewer hands. Expanding the size of the House would restore the power of the people.

In short, it’s arbitrary

What were the contemporary feelings about the cap?

The Census of 1920 was the first to record a population of over 100 million. The population growth and concentration of power created difficulties for Congress in terms of apportionment. Between 1920 and 1929, Congress failed to apportion representation following the Census, which left the Apportionment Bill of 1911 in effect. There were many factors at play, including the shifting of power between large and small states, the space required to seat additional members, and who should be counted for purposes of apportionment. 

The division over who should be counted for apportionment was hotly debated. The “alien” population that concentrated in metropolitan areas shifted representation away from “agricultural states of the South and Middle West and rural New England.”

One side argued that when the founders used the word “persons” in Article I, Section 2, they did so in the “comprehensive sense of all human beings.” However, others argued that in the “Constitution adopted by and for the people of the United States, the word ‘persons’ referred to American persons and that Congress had the power to exclude aliens.”

The Permanent Apportionment Act of 1929 fixed the number at 435, and it determined that apportionment would count all persons regardless of citizenship or legal status. It minimized the effectiveness of the House, delegated the responsibility of Congress to the Executive, and empowered the state legislatures, shifting power away from the people and to the President and States. 

States take advantage of the weakened power of the House with increasingly Gerrymandered districts. The President takes advantage of the unrepresented nature of Congress by connecting with the citizens at large and concentrating the power of the people into the Bully Pulpit.   

Some folks could see the writing on the wall: